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FRANKLIN INSTITUTE 


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Paper Testing Methods 


Microscopical, Chemical and Physical 
Processes and Apparatus Employed 


Prepared by the 
Committee on Paper Testing 
TAPPI 


Price — $3 


Published for the 
Technical Association of the Pulp and Paper Industry 
18 East 41st Street, New York, N. Y. 
by the 
LOCKWOOD TRADE JOURNAL COMPANY 
if EAST 39TH SLREET, 
MEW YORK NY, 


7 Copyright, 1928 
By the Technical. Association of the Pulp and 
ite | . 
Sora hel SUI BRARY of So 


a. | “FRANKLIN 2 
a x09) TINSTELUTE? ae 


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4 24 Kt i ; 
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PREFACE 


The chief functions of the Paper..Testing Committee of the 
Technical Association of the Pulp and Paper Industry are to 
develop and to standardize paper testing methods. 

The early work of the committee dealt entirely with development 
of methods. Many valuable test methods were developed and 
these, together with considerable related information, were pub- 
lished:in committee reports. This pioneering work in development 
of American standards for paper testing was directed by Frederick . 
C: Clark, chairman of the committee. In 1920 the information so 
far developed was published by the Association in a pamphlet by 
Mr. Clark. A revised: edition was published .in 1922. 

After Mr. Clark’s resignation from the committee, the direction 
of the development of .methods was continued by Frederick A. 
Curtis. The committee under Mr. Curtis’s direction added a con- 
siderable number of new: methods required as a result of new 
developments in the industry and contributed considerable addi- 
tional information in general to the technique of paper testing. 

When the present chairman was appointed in 1925, a survey of 
the existing situation showed that the.development of test methods 
required to determine the quality of paper, aside from tests related 
to special uses of paper, had been quite adequately covered. It 
seemed advisable, therefore, to undertake a revision of the existing 
methods with a view to writing them in a standard form and hav- 
ing them adopted by the Association as its official standards. This 
program involved more adequate specification of conditions of test- 
ing, development of uniform nomenclature, statement of tolerances 
and methods of expressing results. The plan was approved at a 
meeting of the committee held at the Bureau of Standards, July 
27, 1925, and the following method of procedure was formulated: 


“MeTHOD OF PROCEDURE FOR ADOPTION OF OFFICIAL PAPER TESTING 
Meraops ; 
by the Technical Association of the Pulp and Paper Industry. 
The work on standardization of paper testing methods will be 
divided as follows: 
Microscopical 
Physical 
Chemical 
Optical 
Tests for Special Uses of .Paper 


“The chairman of the Paper Testing Committee will appoint 
sub-committees dealing with each division of work, the chairman 


4 PREFACE 


of the sub-committees constituting the Paper Testing Committee. 

The program of work for the various sub-committees will be 
formulated by the Paper Testing Committee. After a test method 
specification has received the approval of the majority of the 
sub-committee, it shall be forwarded to the chairman of the Paper 
Testing Committee for the approval of this committee. When 
this is received it shall be forwarded to the secretary of the Tech- 
nical Association for mail ballot of all Members of the Associa- 
tion in respect to adoption or rejection. The majority approval of 
those voting shall be required for adoption. 

Revision of official methods shall follow the same procedure as 
adoption of new methods.” 

The procedure was approved by the Executive Committee of the 
Technical Association. ~A number of official methods have been 
adopted and these are included in this edition of Pager Testing 
Methods. 

Attempt has been made to have this revised edition as complete 
as possible. A number of new proposed methods and testing in- 
struments are described, and much of the text has been rewritten 
wherever found necessary as a result of developments since the 
previous edition. 

B. W. Scrispner, Chairman, 
Paper Testing Committee, TAPP]. 


Members of Paper Testing Committee, 1927-1928: 


ALLEN ABRAMS Ci 10 Uses 

G. R. ALDEN C.-L. burein 
A. L. ALLEN G. J. Manson 
A. E. BACHMANN F. A. Miran 
T. C. BENTZEN J. E. Minor 
E. A. BERGHOLTz A. T. RANDALL 
H. E. Brakewoop E. O. REED 

O. W. CALLIGHAN W. O. Roe 

M. L. Caust R. H. Savace 
T. L. CrossLey R. H. Stmmons 
O. S. Ecan H. A. SmitH 
W. N. ENGLER R. H. Stevens 
T. H. Grant Epwi1n SUTERMEISTER 
R. C. GrirFin Cy Reolare 

E. G. Ham D. D. Uonc 
1s Gas & a a C. D. VierGiver 
H. U. Kier P. F. WEHMER 


Contents 


ee A oe og aly oils G/ai ke Soe ad KOS elalb  @ hak ew Oe 3 
TURIN TRA TION So). oi s5ic bes ie fe oe ois lny 6 vite Conn d vans sauce 9 
MOET IN FORMATION icc. Cece ec cece ened vcs vieceecadncdes 1] 
NR IN aM IS rs fo eka ona Kas cials cde > alvcia's Viv ee SW 86 bay 11 

iar operer urchase pecifications ... os... cee eee eta 11 
smistours ot -viethods 35..6...5.5 Peel toners te Warne SNe os Gi; 12 
NU MINCDONS oc ocr vushcisle sn seis Saleen ko he asa nwa i2 
eeeepiies tricia) Method © oesc 2. he ee ce la eee eee 12 

SR EEC ae, Fg AE eo Gok wave aks 40S Ha hep ee Uae a nee 13 
MIME ROSCOPICALLIUXAMINATION .ooce0 cae ewis ere cee evaleies 16 
meeccimination of Hiber Composition .......5......6. 6. 16 
ARIEL H Oy 98 Tociscy’ Pa. oh oe Sade N si elev odes 16 

PE MUmIVICHnOd ( LeTtative). 6. oie ds «. kale oe cuca bee 21 

Me erative gyLGtNOUS© oo. van he os ge nae 3 nls Seeib eae es 22 
Pmeeuceussion of Wanipulation®... ..c.chck Teeth eee cen 23 
Nee a Edt 1S Bis ee ne ee Uk wb atarvid os wis Lad Gs om 24 

pee assication of Papermaking Fibers. .............0008. 25 
ret CAI Foy os Sus te eh oe soba ON NS oe ees 35 
eR Se tei FP ADCT o,f be nan 6 on nwa cau shed ss ones 35 

Nee MN ei es ste da pa Po aoe hg wee Os b Blac 37 
IE rere UEGTING | 0 os ce ve ed nnle han Cob R eee Cas Poe des 38 
Mee rotcosoL tLiygrometric State .2 2.0.5 eps et ks wee as 38 

a. Temperature and Humidity (Absolute and Relative) 38 
meontnl ot Relative Humidity 2.02.0 e052) .04 kk. 39 

c. Effects Produced by Changes in Hygrometric State. 40 
Peromcial Conditioning ‘Method “ic... fees bak oa 43 
Zoeeaacnine Uirection, Oficial Method -..........05...42. 44 
ei ete CoO GAS CF aRO iS Ae ce 45 
NRE oh ACT pon fists Sa ay Sic ice wines sew dig Aleta «) slew 08 45 
PUR NOR create conv ake te Ng Coats vpn a al is ue Gace 8 45 

Pe IRE eta tl Cal On nie ce sid aneead SRE G eso kee 49 
MT Ot OVONI Ee ACtOL Se ah. Wi cg ov Ris ew Lone e sa be 50 

REE EAL CNIO CN. 5) en ot, os ictal wales 308 b Shape ans Klee 52 
Ne 1LR Fi hte nen anak ys ea ys BE Lida vn VS 52 
USCS VIPS 9 Ye Mller eg Aime ape a mar ra Pa 53 

MH Ce MMMM PT ENG 4 WY SMR E scale ASS Ge picked aed eae S ede 55 


PAPER TESTING METHODS 


6. Thickness, Official Method *.. 05.2. 303. >>» ae eee 55 
7. Balko 2. oe ee Re OA 56 
8. Folding Endurance 2.2... 2. cabs sneo ae 58 
a. General. Information. <0) .u.. daa» oe eee 58 
b. Official, Method « oil. .4ao ss ese ee 58 
c. Calibration. 2a). 6 es des comm seo os eee 62 
d. M.LT.Folding Tester .....6.. «3 nos: « 1 ee 62 
9. Tensile Breaking Strength ..../:+.,+.+-+> see 64 
24. Description ise te 0 adieu bee ale hres ke see 64 
b: Official Method ......000. 58 £455 Soe 66 
c.-Wet Tensile Strength .... 5.00... 0 ~« 68 
10. Tearing Strength, Official Method ....25), 97a eee 68 
11, Wet Rub ooh. .04 hs oe ce a 72 
12, Air Resistance or Porosity. /J.. 1.4 0s fo: 
13. Degree of Sizing 9. ooh 0) i dsaes a se 76 
a. Degree of. Internal: Sizing ..\....2:2 eee 76 
b. Degree of Surface Sizing... 15. 9es eee 2a eee 
14, Water Resistance «13.34 20.0. 53 1 ee 81 
a. Definition... sein ds Ws Oa eee ee ee 81 
b. Bureau of Standards Ground Glass Method ....... 82 
c. Method of A. R. Harvey <. y..3 4 eee 83 
15. Grease Resistance... 6: 73.200 2s 85 
16. Penescope -...004. 500. pe csew cues s A en 4288 
17. Absorption 2.6.5 00... 0. 5.0bees bene Gea eee 89 
A. Strip. wie basa cdlgw Go als kim ie © fan ee 89 
b. Pipette. 0. 6s eck bee pie a's be 90 
c. Total Absorption ©... i. <.<5 fuss tee oR 
d. Blotting Test 2.2... 0. ..42 ss sec 9D 
18... Opacity: ... sie ic Yew ERs ads ee ee eae 92 
19, Gloss (i .aa ves) ey ea ea ciel alee ae /94 
20. Surface Texture i. ou, .D A aes ne rf 96 
21.. Volumetric Composition’... ..> «5.4.05 45: one .. % 
22.. Conducting “Particles sc) vai van y oe ee Ge a! 7 
23. Extractor and Friction. Cleaner 72.22.20. ae Pee 
24. Retention of Filler ..... 5.2.6... 2.20 ee 
25. Expansion and Contraction of Paper ........, Mae GR Re 102 
a. Schopper Expansion Tester .. :.... 1. s.snsetae ne 102 
b. Davis’s: DeScription i... i..... +0. 5 ee 102 
c. A Simple Procedure ).¢. 0.4.2. 2052.5 oe 102 
d. Expansion of Boards... .:2....4. sae 103 
26. COLO asi sys wos diate 5 | ns aba 0m mie ee ee 104 


27. Stiffness 


core eeecdan eee eee aes & 8 6 He & Ob Se fe 6 6 60! oe) we eee heen 


PAPER TESTING METHODS 7 


DE MA CN ALY STS 005 occ gored os o's win he dian utters ale Delores » 106 

1. Official Method for Quantitative Determination of Mois- 
MM ACE LO Rs tM at, sue Bins Fy va Ok nae Stats 106 

2. Official Method for Quantitative Determination of Ash 
er Ge oe aay alesis a dig nfo Wa wane > veld woe 106 
3. Official Method for Analysis of Mineral Filler In Paper 107 

4. Official Method for Analysis of Mineral Coating of 
PE OU ies tr ge LL dg tc abe, vhs ave nce ae Me hig 108 

5. Official Method for Determination of Amount of Coat- 
micemrenimera) Coated Paper .. 0. seve cee ees baer eee 109 

6. Official Method for Qualitative Determination of Casein 
re er nig een woe Vo ke eee whe 110 

7. Official Method for Qualitative Determination of Rosin 
Hi ELSA Sea lice, One eee A ROAR ee le ner ar we re a 110 

8. Official Method for Quantitative Determination of Resin 
J TESS SSS 50 ey inlets en aa eC aver 110 

9. Official Method for Qualitative Determination of Nitro- 
@-nous Proteimaceous Materials in Paper..............- 2 

10. Official Method for Quantitative Determination of Pro- 
Pere OUS SO NELTOGEN 1) APETN... Gy fakes «spies ble oe ne en 2 

11. Official Method for Qualitative Determination of Starch 
PR et ee dna st ian eh Pianos «5k ace de 2 113 

12. Official Method for Quantitative Determination of 
rN ORT Me ck 05 cd et Wa cS Pts oa via Rd os cw ER 114 

13. Official Method for Quantitative Determination of Ac- 
Pea Mire er eh eo yc bil tow he sae oud hn os 8 LES 

14. Official Method for Quantitative Determination of 
Pewesoite viet aramned Paper |... iia. ci. ecco vow oh eee. 116 
emcee rig Matter, oie. 6. Seen eet a ay al awe oe 7 
Pemeectareorespecial: Materials (50.0.6 cds ee oa os oe 117 
Met CNN 11) EP ADET nce occ eas hoe eek tea c visnn ne wadgelts 119 


List of Illustrations 


Figure Title Page 
ME TR ECORT (CARD (toch oe ef since tcslck ce oat Seas cco eee 14-15 
REPRO PH AKER Ac Grud oy Cxiwome Ph FieT alae oie wleeos ly 
DIITOUREREFOR WIICROSCOPE. SLIDES) 2.0... .4 cule d oe wk te a ee 18 
PESO IE AS NITCROSCOPE }2 05025 fawilds pedal Fes sa eb ee dvds 19 
5. CLASSIFICATION AND CHARACTERISTICS OF THE More Com- 

MON VEGETABLE FiRers USED IN THE INDUSTRY ....... 26-27 
6. PHOTOMICROGRAPHS OF PAPERMAKING FrBers (x 100) ...28-32 
7. PHOTOMICROGRAPHS OF CoTTON RaG FIBERS SHOWING PrRo- 
GRESSIVE CHANGE IN STRUCTURE WITH BEATING (x 100) 33-34 
8. VARIATION IN PHYSICAL PROPERTIES OF PAPER WITH 
ete eI UMIDITY Wi Cs sGe rence bh ad webs 42 
9.. PAPER WEIGHING DEVICES: 
eS, UII CUNEATE Ee a 8 Gna pa gee I OS 46 
ESOT E Al ANCE rae oc we Oh Sian rece de ae eee 47 
Este ay CUETt  SCAlC RG re ass keer ie ba deel sant als 48 
Puc weal bealh, SCAle Gc AM owe kee eae cape oe 49 
10. Burstinc STRENGTH TESTERS: 
ee eae ooh te eet oe oh phe ho Seecue acc aoe liavaiel Huela 51 
ie, cle EE 2 Ai Eel dis as a a oO eM I eta a 51 
NTS OCG Pe ee a. ER od hs Cha ake eek « 52 
er eraser ea ek OE eS oe eget ce bivhintn CoP es 33 

IAC PICK NESS. MICROMETER i. 5624 cas ec dee oom 55 
Ne APRA Bitsy, cacy sd wk wid a anid ig Wiese de woaktiels wane we Yale 57. 

Toa SeCMOPrER FOLDING ENDURANCE TESTER ......:.00 00: s004) 58 
14. Beti-CrANK LEVER FOR CALIBRATING SCHOPPER FOLDING 

RNC MeL ESTERS Mo oie mae ke ei oh Me oa we we « 61 

Peete ee OLDING EENDURANCE LESTER... 2.0: cis- csc eens 63 

16. TENSILE BREAKING STRENGTH TESTERS: 
CIE ge ae Re cate ota Uae te Sak cote Shes Ob 65 
MPS Cette eet et et nt dks Peo S28 ac OD 
PE MOG ETI Sr eS ahaa re gon asia Gi eee sete re tue eet oA 66 
CE SCIOTO Si ieran Oe duis reece ah eed we eae EE oe 67 

PP EMENDORE | HARING: LESTER ... vids ce ee dees Wea vee tenses 69 

18. BureAvu oF STANDARDS MODIFICATION OF THE ELMENDORF 
TEARING TESTER FOR INCREASING ITS CAPACITY ....... 71 

Pe OL RS TER ool sede Cae «ce k a tacts oe ee yeas 72 

20. Arr RESISTANCE TESTERS: 

Rta OS LIE Ys LEM SOITICLOTS y's wet tra, soe ts ie ge ike aha winte 73 


10 PAPER TESTING METHODS 


20b. Schopper: Densometer) .)..5. 33... 2 ee 74 
20c. Emanueli Porosimeter <..........1.2 9. 75 
212 VattEY Size TESTER: 2.00. «<5 on oe 77 
22.'> Curt Sizinc® TESTER, ..24..5. 0s vn ek eee 78 
23. Dry-INbDIcAToR SIZING, TEST: METHOD ... )225) 0s eee 80 
24. Grounp GLass WATER RESISTANCE TEST METHOD ....... 82 
25. Harvey WATER RESISTANCE TEST METHOD ............. 83-85 
26. APPARATUS FOR GREASE RESISTANCE TEST ..:.........--- 86 
27. THE PENESCOPE, AN APPARATUS FOR TESTING RESISTANCE 
TO. LIQUIDS 6d 4s 4 doen Sy ws led el abd oe 87 
28a. ABSORPTION TEST; KLEMM METHOD ........ 0.3 88 
28b. DaLen BuoTrinG Paper TESTER +... .-241, see 91 
29. OPACITY TESTER ..50.. cee 00s 0s pee os eee 92 
30. INGERSOLL GLARIMETER <2... 00.012 des eee 95 
31. APPARATUS FOR DETECTING CONDUCTING PARTICLES ...... 98 
32. EXTRACTOR AND FRICTION CLEANSER.,)....csape oe 99 
‘33. SCHOPPER EXPANSION TESTER 2.5.4 55. Gu eee 101 
34. GRIFFIN "EXPANSION ‘TESTER [V2 4:5. .... 0 eeuoe ee 103 


BOARDS oe Ove na decd pwnd es eae 104 


PAPER TESTING METHODS 


I. GENERAL INFORMATION 


1. Purpose 

The testing of paper is usually performed for one of four 
reasons and it is possible that methods suitable for one purpose 
may not be suitable for another. These purposes are: 

(a) To study the manufacturing processes respecting their im- 
provement or improvement in the quality of the paper. 

(b) To maintain a predetermined quality. 

(c) To determine whether the quality is equal to a predetermined 
standard or specification. 

(d) To. determine whether the paper is suitable for a given 
purpose. 

The manufacturer is einterested hae 3 in (a) and (b), eure the 
user or buyer is interested in (c) and (d), when paper is bought 
on specification. Methods may be developed for local use in mills 
for specific purposes related to manufacturing processes which are 
satisfactory for those purposes. There is obviously no possibility 
of standardizing such methods and no need of attempting this. 
However, to permit comparison of manufacturing and research 
data and to obtain comparable results in testing for compliance 
with specifications of quality, it is necessary to establish standard 
testing procedure. One of the main objects of this publication is 
to promote such standardization. Considerable progress has been 
made in this direction. The Paper Testing Committee of the 
Technical Association has developed a large number of testing 
methods in definitely specified form and these, which cover the 
requirements of ordinary testing practice, have been adopted as 
standard by the Association. Such methods are termed “official” 
methods and are so designated in this publication. 


2. Paper Purchase Specifications 

oe merchandising any commodity it is becoming generally recog- 
nized that definite test basis for purchase is the most satisfactory 
system. This tends to prevent delays, legal litigation and other 
annoying and expensive experiences common to transactions based 
on-the personal judgment of the parties involved. With develop- 
ment of adequate test methods the use of paper purchase specifica- 
tions embracing requirements as to certain tests the paper must 
meet adequately, has become quite common. This publication con- 


11 


12 GENERAL INFORMATION 


tains standardized testing methods sufficient for general purchase 
requirements. A number of commercial paper testing laboratories 
are completely equipped for making all tests commonly required. 
A very complete list of the paper specifications in use in this 
country is given in a Directory of Specifications issued by the 
United States Bureau of Standards. The same bureau has issued 
Directory of Commercial Testing and College Research Labora- 
tories which lists all known laboratories that do commercial paper 
testing. 


3. Groups of Methods 


For convenience, the various methods of testing are grouped 
into three classes: microscopical, physical and chemical. 


4. Records and Reports 


Complete laboratory records of all tests should be maintained 
and reports should be made in a systematic manner. Original test 
data should be recorded directly on a test record card which should 
be filed and kept as a permanent record. Printed report forms are 
of assistance in minimizing clerical work and in systematizing re- 
port procedure. The accompanying 5 by 8 inch record card, with 
both sides reproduced (Fig. 1), is offered as a suggestion. Indi- 
vidual requirements, of course, may necessitate modifications in 
this. 


5. Sampling 
Extreme care should be taken in sampling to make certain that 
the sample is truly representative of the lot of paper to be tested, 
that the sample is adequate for the tests desired, and that the 
samples reach the testing laboratory in good condition. The Tech- 
nical Association of the Pulp and Paper Industry official method 
follows: 


OrriciAL METHOD OF SAMPLING PAPER FOR TESTING 
I. Test Sample: 

The test sample, unless otherwise specified, shall consist of 
sheets at least 11 x 11 inches in size, and having a total area of 
not less than 1500 square inches. The sample sheets shall be 
kept flat, free from wrinkles and folds, and protected from ex- 
posure to liquids, direct sunlight and other harmful influences. 

II, Methods of Sampling: 

Not less than 10 per cent of the total number of units, (rolls, 
cases, frames or bundles, etc.), composing a lot of paper, shall 
be sampled if the lot consists of not more than 100 units. If 
the lot consists of more than 100 units, not less than 5 per cent 
of the total number of units shall be sampled. The sample sheets 
shall be so selected from the different units that they will be rep- 
resentative of the entire lot of paper. 


TOLERANCES 13 


The samples shall be taken as follows: 

1. From rolls—The sample sheets shall be taken from the first 
unharmed layer of each roll. 

2. From cases, frames and bundles.—The sample sheets shall 
be taken from the top and center of each case, frame or bundle 
sampled. 

The sample sheets shall be so cut that their edges are exactly 
parallel with the machine and cross direction of the paper. 

III, Resampling: 

In case of necessity for resampling a lot of paper, the samples 
shall be taken as described above, except that the sample sheets 
shall be taken from different units than those previously sam- 
pled. If the identity of the original units is lost, and the paper 
is not in rolls, cases, frames, or bundles, the whole lot shall be 
so sampled that all the different components of it will be rep- 
resented by the test sample. 


6. Tolerances 


In considering test results, tolerances must be allowed for un- 
avoidable variations caused by the inherent non-uniformity of 
paper and by errors inherent in the testing methods. The extent 
of permissible tolerance varies with the nature of the paper and 
of the test used and must be determined for each particular case 
with consideration of these factors. 


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Test Record Card. 


II. MICROSCOPICAL EXAMINATION 


1. Determination of Fiber Composition 
a. OFFICIAL METHOD 


Following is the official Association method for determining the 
fiber composition of paper: 


I. Apparatus: 

A microscope capable of giving not less than 100 diameters 
magnification is necessary for determination of fiber composition. 
It should be of the compound type and have a mechanical stage. 


IT, Specimen: 

1. Composition—-The specimen for test shall consist of pieces 
having a total area of not less than 6 square centimeters (1 
square inch) cut from different portions of the test sample, so 
as to be representative of it. 

2. Preparation for Examination—Place the specimen in a small 
beaker and completely cover it with a 0.5 per cent caustic soda 
or caustic potash solution, heat to boiling, transfer the contents 
of the beaker to a small 200 mesh metal sieve and wash thorough- 
ly with water. Roll the moist pieces of paper into a ball and 
work between the fingers to loosen the fibers. Transfer to a 
test tube and shake until the fibers are completely separated. 
Pour a portion of the mixture into a second test tube and di- 
lute to a fiber concentration of about 0.1 per cent. Transfer 
the fibers to a microscope slide by means of a dropper consists- 
ing of a glass tube 20 cm: (6 inches) long and 6 mm. (% inch) in- 
ternal diameter, fitted at one end with a rubber bulb. Thorough- 
ly mix the fibers and water, quickly insert the dropper into the 
mixture 5 cm. (2 inches) below the surface, expel two bubbles of 
air from the dropper, then fill the tube to a distance of about 
13 mm. (% inch). Transfer the contents of the dropper into the 
slide, making 4 drops, completely emptying it. Repeat this 
procedure until the slide is uniformly covered with drops of the 
mixture, then place the slide in an air-bath until dry. Add 
stain as specified in Section III-2 to the dried fibers and press 
down on them a second slide or large cover glass. Remove excess 
moisture from the edges of the slides with absorbent paper. 
One slide shall be sufficient for ordinary determinations. In 
case of dispute not less than 3 slides, shall be examined. 


III. Method: 


1 Method of Observation. The prepared slide shall be 
examined microscopically observations being made at vari- 
ous points in a straight line, twice lengthwise and four times 
crosswise of the slide, each line of the observation starting at a 


16 


FIBER COMPOSITION 17 


Pion 2: 


Test Tube Shaker Devised by M. B. Shaw, Bureau of Standards, For 
Defibering Micro Test Specimens, 


different point. A magnification of-not” less than 100 diameters 
shall be used. A magnification of 100 diameters is desirable as 
with lower magnification it is difficult to observe the character- 
istic structure and shape of the fibers, both of which aid materi- 
ally, in addition to the color developed by the stain, in identify- 


18 MICROSCOPICAL EXAMINATION 


ing the fibers. The number of each kind of fiber present in at 
least 25 different fields and a total of not less than 200 fibers shall 
be counted, using the diameter of the: field as observed through 
the microscope as the unit of measurement. The amount of 
each kind of fiber present shall be computed as a percentage of 
the total fiber composition. 

2.- Stains. For all purposes except as specified below, either 
the Herzberg or the Sutermeister stain shall be used. These 
shall be prepared and used as follows: 

Herzberg-—Prepare the following solutions: 

(A) An aqueous solution of C. P. zinc chloride saturated 
at 70 degrees F. 

(B) 0.25 grams of C. P. iodine and 5.25 grams C. P. potas- 
sium iodide dissolved in 12.5 cc. of distilled water. 

Mix 25 cc. of solution (A) measured at 70 degrees F. with solu- 
tion (B). Pour into a narrow cylinder and allow to stand until 
clear. Decant the supernatant liquid into an amber colored, glass- 
stoppered bottle and add a small piece of iodine to the solution. 
Thoroughly moisten the fibers with this solution and remove the 
excess with blotting paper. The solution should be tested with 
known fibers and readjusted if necessary by addition of either 
zinc chloride or iodine. The following colors are developed by 
this stain: 


Tobie for there See Holder: 


Pres) 
Holder for Microscope Slides. (Bureau of Standards, Washington, D. C.). 


FIBER COMPOSITION 19 


Fic. 4. 


Binocular Microscope. 


Red—Linen, cotton, bleached manila hemp. 

Blue—Chemically prepared fibers low in lignocellulose, from. 
wood, straw and esparto. 

~Yellow—Fibers high in lignocellulose such as groundwood, 
jute, and unbleached manila hemp. 

Sutermeister—Prepare the following solutions : 

(A) 1.3 grams iodine and 1.8 grams potassium iodide dis- 
solved in 100 cc. of water. 

(B) A clear, practically saturated solution ‘of calcium 
chloride. 

In using this stain, apply solution (A) after moistening the 
fibers with water, allow to remain about one minute, remove the 
excess by blotting and then add solution (B). 

The colors developed by the Sutermeister stain are, in general: 

Red or brownish red—Cotton, linen, hemp, ramie. 

Dark blue—Bleached soda pulps from deciduous woods. 

Bluish or reddish violet—Bleached sulphite fibers and thoroughly 
cooked unbleached sulphite fibers. 

- Greenish—Jute, manila hemp and the more (eae fibers in 
unbleached -sulphite. 

Yellow—Groundwood. 

Lofton-Merritt—This stain shall be used for differentiating 


20) MICROSCOPICAL EXAMINATION 


between unbleached sulphate (kraft) and unbleached sulphite 
fibers. It shall be prepared as follows: 


(A) Malachite green, 2 grams. Water, 100 cc. 
(B) Basic fuchsine, 1 gram. Water, 100 cc. 


These shall be mixed in the proportion of 1 part (A) to 2 
parts (B). As dyes from different sources vary it is necessary 
to test them by staining known fibers. Unbleached sulphate 
fibers are stained blue or blue-green and unbleached sulphite 
fibers purple or lavender. If any purple fibers appear in un- 
bleached sulphate fibers, this indicates there is too much fuch- 
sine present and more malachite green solution must be added. 
The opposite is indicated if some unbleached sulphite fibers de- 
velop a green or blue color. 

The Lofton-Merritt stain shall be used as follows: Add the 
compound stain to the fibers and allow to remain 2 minutes. Re- 
move excess stain by means of a hard filter paper and add a 
few drops of 0.1 per cent hydrochloric acid. After about 30 
seconds remove the excess acid. Next add a few drops of dis- 
tilled water and remove the excess. 


Bright Stain—This stain shall be used for differentiating 
between bleached and unbleached fibers. The solutions required 
are: 

(A) 2.7 grams ferric chloride (FeCl;s6H2O) per 100 cc. dis- 
tilled water. 

(B) 3.29 grams potassium ferricyanide (K;Fe (CN).«) per 
100 ce. distilled water. 

(C) 3 grams of crude (not treated with sodium carbonate) 
substantive red dye per 500 cc. of distilled water. The 
dye used shall be DuPont Purpurine 4 B. Concentrated, ° 
or its equivalent. 


These solutions must all be made with cold water. 


Filter solutions (A) and (B) and keep in separate stock bottles 
at a temperature not exceeding 20 degrees C. Make solution (C) 
fresh each day it is used. For staining use tall narrow beakers 
suspending the microscopic slides in the beakers from clamps. 
Mix 10 cc. each of solutions (A) and (B) in one beaker and add 
an equivalent amount of solution (C) to another beaker. Set 
the beakers in a water bath, the temperature of which must be 
maintained constantly within + 1 degree of 20 degrees C. Place a 
thermometer in the stains. When their temperature is 20 degrees 
C.. dip the slide containing the dry fibers in distilled water to 
moisten it uniformly (so that no air bubbles will be formed when_ 
it is stained), then place the slide in stain (A-B) and allow it to 
remain 20 minutes. Wash by dipping in distilled water six times, 
then renew the water and repeat the washing process. Dry the 
contents of the slide and repeat the processes of moistening, stain- 


FIBER COMPOSITION 21 


ing, washing and drying, using the (C) stain. It is desirable to 
fix the top glass on the fibers with a drop of balsam. 

The colors developed by the Bright stain are: 

Red—Bleached fibers or fibers practically free from lignocellu- 
lose. 

Blue—Unbleached fibers or fibers containing lignocellulose. 


IV. Report: 

The proportion of the various fibers found shall be reported 
in terms of percentages of the total fiber composition, to the 
nearest 5 per cent. The following nomenclature which covers 
the fibers commonly dealt with shall be used in reporting re- 
sults: Chemical wood fiber; chemical deciduous wood fiber; 
chemical coniferous wood fiber; groundwood fiber; manila fiber; 
jute fiber; rag fiber; linen fiber; cotton fiber; esparto fiber; 
straw fiber. 7 
V. References: 


“Microscopic Paper Fiber Analysis.”’—G. K. Spence and J. M. Krauss. 
Paper 20. No, 11, 11) (May 23, 1917). 

Paper Priifung, Wilhelm Herzberg. 

Chemistry of Pulp and Paper Making.—I, Sutermeister, page 390. 

“Method for Differentiating and Estimating Unbleached Sulphite and Sul- 
phate Pulps in Paper.’’—R. E. Lofton and M. F. Merritt, Technologic Paper 
No. 189, U. S. Bureau of Standards. 

“ “Microscopy of Paper Fiber.”,—C. G. Bright. Paper 20, No. 25, 11 (Aug. 
29, 1917). As modified by the author, 


b. Dor MErHop (TENTATIVE) | 

To avoid the undesirable personal equation involved in estimating 
the relative sizes of the fibers, the following method of counting is 
recommended for trial with the view to future adoption as the 
official method if found satisfactory. This is known as the dot - 
method, a disk containing a dot or point being placed on the 
diaphragm of the eyepiece, and the fibers being counted as they 
pass under the dot. It is possible to construct a satisfactory cross 
line disk by the use of two silk fibers, approximately 0.01 mm. in 
diameter obtained by untwisting silk thread. The fibers are drawn 
across the center of a round cover glass 18 mm. in diameter at 
right angles to each other. They are cemented to the edges of 
the glass with paraffin or other adhesive and the protruding ends 
cut off. The cover glass is then placed, with the fibers on the 
underside, on the diaphragm of the microscope eyepiece. The 
cover glass is then centered on the diaphragm of the eyepiece of 
the microscope and cemented in this position with a drop of 
paraffin. A graticule or crossline disk is carried in stock by many 
manufacturers of optical equipment. It consists of a round thick 
disk of optical glass on which are engraved two lines at right 
angles to each other, both lines running completely across the 
disk and intersecting at the center. Place the crossline disk on the 
diaphragm of the eyepiece of the microscope and a prepared slide 
of stained fibers on the mechanical stage. Starting at one end of 
the slide: about a quarter of the way down from the top, move 


22 MICROSCOPICAL EXAMINATION 


the slide in a straight line throughout its entire length by means 
of the mechanical stage. In moving thus through the field of 
view each fiber or part of a fiber shall be counted which passes 
directly under the dot or point formed by the intersecting cross 
lines on the disk. Some of the fibers may be long and pass under 
the point twice or more but they shall be counted each time. If 
aggregations of fibers such as occur in groundwood are encoun- 
tered the number of single fibers in the aggregation shall be esti- 
mated and. counted as if the fibers. were completely separated. 
Select another path across the slide about half way down from 
the top. Repeat. the entire counting process adding the results to 
those obtained foregoing. Repeat again over a path about three- 
quarters of the way down from the top of the slide. Add the 
results to the foregoing. Select two or more up and down paths 
and repeat the process. The record of the count may be made 
conveniently in either of two ways: (1) By making separate 
columns for each kind of fiber observed in passing over the slide 
and entering a record in the proper column as soon as a fiber 
passes under the dot. (2) By making a complete trip across the 
slide counting only one kind of fiber, e.g. rag. A return trip is 
then made over the same path counting only another kind of 
fiber, e.g. chemical wood. In this way successive trips are made 
over the same path until every kind of fiber present has been 
counted and the results for a given fiber are recorded after each 
trip. 


c. ALTERNATIVE METHODS 

1—Estimation Method: - The estimation method involves train- 
ing the eye by the comparison of unknown samples with standard 
mixtures of known composition. Accuracy in the estimation 
method requires considerable practice and continual reference to 
the standard mixtures. Although this method gives accurate re- 
sults when used by experienced analysts, the actual counting of 
the fibers is specified in the official method as counting is con- 
sidered a more practicable procedure for general use as it enables 
comparatively inexperienced operators. to obtain ‘satisfactory 
results. . . { 

2—Spence and Krauss Method: A third method of fiber analy- 
sis is the fiber-weight-length method proposed by Spence and 
Krauss: The slide is placed under a microscope of 160 diameters 
and the length of the various fibers is measured in terms of the 
diameter of the field seen through the microscope. The total 
length of each kind of fiber present multiplied by its weight factor 
gives a set of results that are directly comparable and may be 
converted into per cent of each kind of fiber present. The weight 
factors as determined by the originators of the method are: Rag, 
1.000; hemlock, 0.870; poplar, 0.454; birch, 0.652; beech, 0.525; 
maple, 0.365. It remains to be proven whether these factors or 


FIBER COMPOSITION a 


any factors are general applicable to fibrous raw materials 
from different sources. It presents possibilities, however, in the 
direction of securing increased accuracy. 


d. Discussion oF MANIPULATION 

The following suggestions are offered to those just beginning 
these tests: 

It is absolutely essential to have a satisfactory stain or else the 
results will be worthless. To test out a stain make up a mixture 
of about equal parts of bleached soda pulp, bleached sulphite pulp 
and rag filter paper. Prepare a microscope slide from this mixture 
and stain with the stain to be tested. If the stain is correct, then 
the soda pulp should show a dark blue color, due to the thicker 
and more opaque fiber walls; the sulphite pulp should show a 
light blue, due to the thin fiber walls; and the rag fibers will show 
a red or wine-red color. If the blue color is more of a violet, 
then too much iodine is present and more water or zinc chloride 
should be added. Zinc chloride produces the blue color, iodine 
produces the red and the yellow colors and the addition of water 
serves to weaken the color that predominates. 

In some cases where it is necessary to examine all grades of 
paper, it is advisable to keep several stains on hand. A stain that 
gives the best color on groundwood and bleached sulphite seldom 
gives a correct color on mixtures of rag, bleached sulphite and 
soda pulps. In such a case, make up one stain so that it will give 
a bright lemon yellow on a known sample of groundwood pulp and 
a slightly greenish blue on unbleached sulphite. For the mixture 
of rag, bleached sulphite and soda pulp, so adjust a second stain: 
that the rag shows as a clear wine-red, the sulphite as a blue, and 
the soda fibers as a dark blue. In testing out a stain always have 
on hand authentic samples of pulp so these mixtures may be 
made up. : 

To check estimates of fiber analysis, slides of fibers in known 
proportions are made. Pure stock is beaten in a small beater and 
made into hand sheets. Sheets of the various pure fibers are 
kept under the same atmospheric conditions. To make up a field 
of known composition take weights of the pure fiber sheets and 
make up a total of at least 5 grams in proportions to give the 
percentage desired. Disintegrate and mix thoroughly by shaking 
with shot in a bottle or by the action of a small disintegrator. 
Sample and make up the slide as for any disintegrated paper 
sample. 

The estimation of the fiber content is based on the relative pro- 
portion of the kind of fibers contained therein, expressed on the 
percentage basis, considering the total fiber content as 100 per 
cent. In making a fiber estimation no account is taken of the 
per cent of clay, alum, size, etc., that may be contained in the 
paper. 


24 MICROSCOPICAL EXAMINATION 


For best results for microscopic work a clear north light is 
desirable and is to be preferred. However, where there is a large 
amount of routine testing that must be done, it is more advisable 
to have a more constant source of light. There are various types 
of lamps available but good results can be obtained with a Mazda 
nitrogen-filled lamp of 150 watts. It is necessary, however, to use 
a blue “daylight” filter in that case. It is to be noted that the 
color of the stained fibers on the slide will be somewhat different 
for the two kinds of illumination. 

A set of colored plates has been prepared by the Bureau of 
Standards of the Department of Commerce, illustrating eight 
paper fiber compositions as seen under the microscope. They are 
intended to serve as reference standards for use in the identifica- 
tion of paper fibers and in the estimation of the fiber composition 
of the paper. These plates are published in Technologic Paper 
No. 250 of the Bureau, entitled Pulp and Paper Fiber Composition 
Standards. It is frequently desirable to make photomicrographs 
of fibers examined as these serve as a permanent record. For 
information on equipment and the use of it for this purpose it is 
suggested that analysts consult the Bureau of Standards Techno- 
logic Paper No. 217, The Photonucrography of Paper Fibers. 


e. SPECIAL STAINS 

In addition to the stains used for determination of fiber compo- 
sition as given in the official method, the following stains are used 
to detect presence of groundwood fiber, being applied directly to 
the paper under examination. 

Phloroglucinol: Dissolve 5 grams of phloroglucinol in a mix- 
ture of 125 cc. of distilled water and 125 cc. of concentrated hydro- 
chloric acid. The solution should be kept in the dark as much as 
possible as it is prone to lose its staining property on exposure to 
light. This solution produces a magenta or wine-red color on 
mechanical pulp. The color may be easily noted by applying some 
of the stain to a piece of newsprint paper. There is approximately 
80 per cent of mechanical pulp in newspaper so that a deep ma- 
genta color is developed. The depth of color is an indication of 
the amount of mechanical pulp present. A very light shade of 
color, however, does not necessarily prove the presence of me- 
‘chanical pulp as partly cooked jute, partly cooked unbleached 
sulphite pulp, and some other fibers are also slightly colored. 


An additional formula is as follows: 


Phiotoglucine 4.4.08 2 grams 
Alcohol, (95. per: cent) 2. 100 ce. 
Concentrated HCL. ............ eet a Oe 


Aniline Sulphate: Dissolve 5 grams of aniline sulphate in 50 
cc. of distilled water and acidulate with one drop of concentrated 
sulphuric acid. This stain produces a yellow color on papers 


CLASSIFICATION OF FIBERS 25 


containing a large percentage of mechanical pulp. This stain is 
not quite so sensitive to mechanical pulp as phloroglucinol, but it 
is easier to obtain and prepare. 

Para-nitroantline: Saturated solution in concentrated hydro- 
chloric acid. This stain produces an orange yellow color in the 
presence of mechanical pulp and other lignified fibers. 


2. Classification of Papermaking Fibers! 


For convenience in studying fibers it is desirable to know re- 
lations of the various groups and the accompanying chart (Fig. 5) 
indicates the arrangement of the fibers that are used for paper 
making. It is to be understood that this is not a botanical classifi- 
cation and any standard textbook on botany is to be consulted if 
this information is desired. : 


CLASSIFICATION OF PAPERMAKING FIBERS 
A. Seed hair fibers—fibers which grow on seeds...... Cotton 
Flax 
Hemp 
Jute 
B. Bast fibers—from the inner bark of trees, shrubs ) Ramie 
TICE TATE Seer heer te. oh era Se cee py Gee” a chpae Wagnds wale cgseis Kodzu 
; Mitsumata 
Gampi 
New Zealand flax 
Abaca 


Sisal 
C. Leaf fibers—from the leaf or leaf stem............ Aloe, American 


(Century plant) 
Pineapple 


Wood fibers, 

coniferous 

Wood fibers, 

D. Stem fibers—from the main stem or trunk of the deciduous 


VERRAN WWE gues ee Ceca mca ae aera ar Straw 
Esparto 
Bagasse 
PETC DELS Metin (Hue fh, sii sic.c'sgl io. siiwiaiesiatece 8 aie Miagie ae hs Cocoanut 
In addition to the vegetable fibrous raw materials, wool is com- 
monly used for paper making. It is usually found in building felt. 
Following are the characteristics of wool fibers. 
Dimensions—Length, 25 to 200 mm.; diameter, 0.010 to 0.100 mm. 
Microscopic appearance—Under even moderately low power of 
magnification (50 diameters) the epidermal scales on the surface 
of the fiber can be seen. Neither silk nor any of the vegetable 
fibers have this appearance. The scales are more or less trans- 
lucent in appearance, and permit the under cortical layer to be seen 
through them. The medulla, commonly called the pith from its 
analogous structure in plant stem, can usually be seen in the 
coarser fibers. 
Micro-chemical reactions—Iodine-zinc-chloride solution, pale 
yellow; nitric acid, deep yellow color; concentrated hydrochloric 
or sulphuric acid, gradually dissolves with red coloration. 


1 “Vegetable Fibers Used in Papermaking.'’"—F, C. Clark, Paper 23, folio p. 
944 (Feb, 26, 1919.) 


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27 


s (Deciduous). 


iber 


pen) Wood F 


s 


(A 


ferous). 
Fibers (x 100). 


bers (Coni 


i 


Hemlock Wood F 


ing 


ak 


Photomicrographs of Paperm 


28 


IG. VOC, 


Spruce Groundwood Fibers (Coniferous). 


Fic. 6d. 
Pine Wood Fibers (Coniferous). 


Photomicrographs of Papermaking Fibers (x 100). 


29 


Fic 0e 
Cotton Rag Fibers. 


Fic. 6f. 
Hemp Fibers. 


Photomicrographs of Papermaking Fibers (x 100). 


30 


Fic. 6g. 
Jute Fibers. 


Fic. 6h. 
Wool Fibers. 
Photomicrographs of Papermaking Fibers (x 100). 


31 


Fic. 61. 
Esparto Fibers. 


Rice Straw Fibers. 


Photomicrographs of Papermaking Fibers (x 100). 
32 


Fic. 7b. 


Photomicrographs of Cotton Rag Fibers showing Progressive Change in 


Structure with Beating (x 100). Fig. 7a. shows the fibers at the start 

of the beating and Fig. 7d. shows their condition at the completion of 

the beating, the other two figures showing their condition at equal inter- 
vals between these extremes. 


33 


Pics 7G, 


Photomicrographs of Cotton Rag Fibers Showing Progressive Change 
in Structure on Beating (x 100). 


34 


| BEATING 35 


3: Degree of Beating 

By a careful examination of the fibers under the microscope it is 
often possible to determine something of the amount .of beating 
to which the stock has been subjected. The length of the fibers, 
the amount that the ends have been frayed and the degree of 
the breaking down of the cell walls all give information in regard 
to the beating treatment. It is necesssary, however, to have con- 
siderable experience before the results are reliable. The use of 
photomicrographs assists in this study and the accompanying plates 
(Fig. 7) indicate some of the characteristic differences of fibers 
caused by the beating treatment. | 


4. Specks or Dirt in Paper 
The appearance of a sheet may show imperfections caused by 
foreign materials or malformation on the wire. These are the 
most common causes of poor looking paper. 


Generally, specks need microscopic examination. A Bausch and 
Lomb binocular microscope shown in Fig. 4, and a set of dissect- 
ing needles are useful. For chemical tests on small particles small 
test tubes made by sealing one end of small glass tubing are con- 
venient if the reaction is to be watched under the microscope. 


RuBBER.—This is very objectionable. It finds its way into the 
stock along with rag stock, sometimes as rubber paste in tire 
fabrics and the like, and sometimes in paper stock as rubber bands 
from office waste. 

Under the magnifying glass rubber specks can be stretched by 
pinning down one end with a dissecting needle and pulling out 
the speck with another needle point. | 

Rubber specks will give a characteristic rubber odor if burned by 
sticking them into a flame on the end of a needle. They are 
soluble in carbon tetrachloride. 


Rostn Specks.—These are translucent, amber colored specks so 
resembling rosin that they are easily recognized. Proof of their 
identity can be had by dissolving the separated speck in ether in 
a small tube so that the action can be watched under the micro- 
scope. Qualitative rosin tests can be applied to the speck as. given 
under qualitative tests for rosin. 

Other specks resembling small bark eM age may come from 
size which was made from impure rosin without proper filtration. 
Although not as translucent as the ordinary rosin speck they 
usually carry enough rosin to respond to the qualitative test. 


Woop Specxs.—Chips or wood fibers which might result from 
the accidental grinding off of a beater paddle or similar cause can 
be quickly identified by applying phloroglucinol; they give a char-. 
acteristic red coloration as in the groundwood test. 7 


36 MICROSCOPICAL EXAMINATION 


Iron Specks.—Washer or beater bars, jordans, scaly pipes, cor- 
roded overhead ironwork, and iron buttons from rags contribute 
iron in metallic or oxidized form at times. The metallic particles 
will be attracted by a magnet after being freed from the sheet. 


The scale or oxidized iron can be dissolved in hydro- 
chloric acid and a drop of potassium sulphocyanate added. Iron 
gives a characteristic wine-red color. This test can be applied to 
the separated particle in a small tube, or the sheet believed to con- 
tain iron may be placed on a glass plate, wetted with concentrated 
hydrochloric acid for five minutes and then with 10 per cent 
potassium sulphocyanate solution. Each iron speck shows red 
when the sheet is held up to the light. The glass plate forms 
a convenient holder for the sheet. The red color fades in a few 
minutes and count should be taken immediately. 


Another method is to immerse the paper in 2 per cent potassium 
ferrocyanide, then in 2 per cent acetic acid, then wash well in 
water. Hang the sheets vertically until dry. There will be a blue 
coloration wherever there is an iron speck in the sheet. This 
method makes a more permanent record than the sulphocyanate 
treatment. 


Or. Spots.—Oil spots are translucent and can be spread or 
thinned with ether or chloroform. Extraction with either of these 
solvents removes the oil, unless it is of a peculiar pasty formation 
caused by use of oily rags in the stock. Mineral oil in rags is 
prone to form a dirty, congealed mass in the washers, which 
specks the halfstuff with black specks in which the mineral oil is 
the binder. Such specks in the finished sheet are not entirely re- 
moved by ether or chloroform. They are slightly translucent, and 
unaffected by solution in concentrated sulphuric acid. 


Cotor Srots.—Poorly ground colors give a fine, specky appear- 
ance usually identified by color only. 


ALuM Spots.—These are usually pulverized by the pressure of 
the calender rolls. They are soluble in water and give a slight 
acid reaction with indicators. This reaction is best watched by 
dissolving the speck in a very small test tube and adding the indi- 
cator while the tube is under the microscope and against a white 
background. 


Coat ParticLEs.—Coal dust is insoluble and gives no color re- 
actions with any reagent. In appearance iron scale can be mis- 
taken for it, and in doubtful cases an iron test should be made on 
the sheet and the unaffected black particles examined for coal. 

Under the microscope it can be seen that coal particles in a cal- 
endered sheet have been so pulverized by the pressure of the rolls 
that they shatter very easily when picked with a dissecting needle. 


STARCH 37 


Large particles give a characteristic black smear when crushed 
and rubbed across the sheet. 

Button Specks.—Bone buttons ground by beaters or jordans 
into small pieces appear in the finished sheet as light colored, 
powdered spots because of crushing in the calenders. A hole is 
often made by a button speck due to the particle piercing the sheet 
and then partly crumbling out after calendering. Such specks 
can be differentiated from alum as they are insoluble in water 
and give no acid reaction with the indicators. 

PAPER SpECKS.—In stock made from old papers small, unde- 
fibered pieces may slide through the screens and form specks on 
the sheet. Such specks are fibrous and when lifted out of the 
sheet they can be defibered under the microscope with dissecting 
needles, showing their identity by this characteristic. 

Foam Spots.—Because of the depression left after each foam 
bubble there is a circular spot more translucent than the rest of the 
sheet formed wherever foam bursts on the partly formed sheet. 
The result is characteristic, the spot being circular and translucent, 
similar to a small, round watermark. 

Drac Spotrs.—Stock adhering to the slices on the wire forms 
small, uneven lumps when it drags off upon the sheet. These spots 
are not very common but can be recognized as irregular forma- 
tions having no foreign material present. 

Kwnots.—Fabrics in rag stock with knotted threads very often 
show the knots in the finished sheet. The knotted thread is easily 
recognized under the microscope. 


5. Starch 


In addition to chemical tests for the determination of starch in 
paper, it is possible to determine the kind of starch used. The 
various untreated starches have characteristic shapes and markings 
which may be easily identified under the microscope. This is. also 
possible in some cases with treated starches used in the tub size. 


III. PHYSICAL TESTING 
1. Influence of Hygrometric State 


Paper, in common with other hygroscopic materials, experiences 
certain changes. in its physical properties in consequence of the 
changing hygrometric conditions of the surrounding atmosphere. 
As the fibers of paper absorb increasing amounts of moisture they 
increase in diameter and become more pliable, but suffer a loss in 
felting strength or bonding ability. Such alterations in the fibers 
affect the strength and many other physical properties of the paper. 
The effects are considerable and follow very rapidly upon the at- 
mospheric changes so that it is necessary to carry out most 
physical tests on paper in an atmosphere of definite hygrometric 
state. 


a. ‘TEMPERATURE AND Humipity (ABSOLUTE AND RELATIVE) 


The amount of moisture in the air (the weight of moisture per 
unit. volume of air) is often referred to as the absolute humidity. 
The term relative humidity, which is more often encountered, 
refers to the amount of moisture in the air relative to the amount 
which it is capable of containing and is expressed as the per cent 
saturation of the air with moisture at the existing temperature. 


The results of numerous experiments indicate that the amount 
of moisture in paper and those physical properties which are 
affected by moisture content bear no definite relation to the amount 
of moisture in the air (absolute humidity), but are governed by the 
relative humidity of the atmosphere. With a constant relative 
humidity the effect of temperature is comparatively small. Ac- 
cording to available data a change in temperature of 10 degrees 
with constant relative humidity has about the same effect on paper 
as a change in relative humidity of 1 or 2 per cent at constant tem- 
perature. It is therefore desirable in the control of the hy- 
grometric conditions for paper testing to give more attention to 
maintaining a constant relative humidity than to maintaining a 
constant temperature. It is, however, desirable to maintain both 
humidity and temperature constant and TAPPI has adopted 65 
per cent relative humidity and 70 degrees F., as the official 
standard hygrometric state for the testing of paper, this hy- 
grometric state having been used for many years both in this 
country and abroad. The relative humidity of the natural or un- 
conditioned atmosphere varies considerably both seasonally and 
diurnally. It is sometimes as low as 10 or 15 per cent in steam- ~ 
heated rooms during the winter and at times during the summer 
it is well above 90 per cent. During the day it is normally highest 
in the early morning hours, falling to a minimum value for the day 
at midafternoon. Because of this daily fluctuation in relative 
humidity and because considerable time is required for the 


38 


PYGROME TRIG = STATE 39 


moisture content of paper to come to equilibrium with the prevail- 
ing hygrometric condition, tests requiring hygrometric control are 
not reliable if carried out in the natural atmosphere of the labora- 
tory even though the relative humidity is determined and the re- 
sults are referred to tables or curves for correction. 

b. ContRroL or RELATIVE Humuipity 


Maintenance: Some of the more important means of maintain- 
ing constant humidity are: 


(1) Air is saturated with moisture by blowing it through a 
spray of water at the dew point temperature corresponding to the 
desired temperature and relative humidity and is then heated to the 
desired temperature, which lowers the relative humidity to the 
desired value. 

(2) Moisture from a steam or water spray is mixed with the 
air until the desired relative humidity is obtained. The apparatus 
may be either automatic or hand controlled. The temperature 
may also be automatically controlled, the two control systems being 
more or less independent. In order to make a device of this 
nature more generally useful a dehumidifying apparatus may also 
be added. Moisture is removed from the air either by passing 
the air over brine coils which condense a part of the moisture, or 
by passing it over a desiccating agent, such as calcium chloride. 

(3) Two streams of air, one relatively moist and the other 
relatively dry, are mixed in the proper proportions to produce the 
required relative humidity. 


(4) Air is exposed to a suitable solution having definite relative 
vapor pressure corresponding to the relative humidity desired’ 
until the air comes to hygrometric equilibrium with the solution. 

Automotic control of temperature may be used in connection 
with any of these methods of controlling relative humidity. 
References: 


“Testing Section, Government Printing Office’—Paper Trade Journal 79, 
No; 18 COct. 30,1924). 

“The Design, Construction and Use of a Constant Humidity Room’’— 
ite Launderers’ Research Association, 17 Lancaster Gate, London W. 2, 

ngland. 

“A Small Constant Humidity Testing Cabinet’—F. T. Carson, Paper Mill, 
March 13, 1926; Technical Association Papers, Series IX, No. 1, Technical 
Association of the Pulp and Paper Industry, New York. 

““A Constant Temperature and Humidity Room for the Testing of Paper, 
Textiles, Etc.”’—-F. P. Veitch and E. O. Reed, Journal of Industrial and 
Engineering Chemistry 10, No. 1, 38 (Jan. 1918); Paper 21, No. 23, 174 (Feb. 
Esso L918). 

“Notes on Temperature and Humidity Control Cabinets’’—Circular No. 310, 
May 1927, American Paint and Varnish Manufacturers’ Association, 2201 
New York Avenue, Washington, D. C. 

“Constant Humidity Testing Room’’—H. T. Ruff, Paper Trade Journal, 85, 
No. 8 (Aug. 25, 1927). 


Measurement: No apparatus for maintaining constant relative 
humidity has been so perfected as to dispense with frequent mea- 
surement of the relative humidity. Of the many methods and de- 
vices which have been used for measuring humidity—the wet and 


40 PHYSICAL TESTING 


dry bulb psychrometer, the hair hygrometer, the dew point appara- 
tus, gravimetric or volumetric determination of the moisture in the 
air, electrical resistance hygrometer, refractometric hygrometer, 
thermal conductivity hygrometer, spectroscopic hygrometer and 
rigidity measurements of vegetable fibers—the simplest and most 
satisfactory means of confirming the relative humidity is the use 
of the ventilated wet and dry bulb psychrometer for accuracy 
and the recording hair hygrometer for constancy of relative hu- 
midity. The thermometers used in the psychrometer should be 
graduated to tenths of a degree, the wet bulb should be com- 
pletely covered with a tight fitting wick of clean muslin or silk 
and should be ventilated at a rate of not less than 3 meters per 
second. A table or chart is used for finding the relative humidity 
from the thermometer readings. The. hygrometer should be fre- 
quently calibrated against the psychrometer. 

A discussion of this subject, together with a lengthy bibliography 
is contained in the following publication by Ewing and Glazebrook, 
“The Measurement of Humidity in Closed Spaces,” Proceedings 
Physical Society (London) 34, No. 192, pages I-XCV (Feb. 15, 
1922). (It can be obtained in pamphlet form as Special Report 
No. 8, Food Investigation Board, Department of Scientific and In- 
dustrial Research, London). 

c. Errects PropucepD BY CHANGES IN HyGROMETRIC STATE 

A brief outline is given following of the principal effects upon 
the physical properties of paper which are produced by fluctuations 
in the hygrometric state. 

Moisture Content: If moisture content is plotted against relative 
humidity the first half of the curve resembles an absorption curve, 
the moisture content increasing rapidly at first with increasing 
relative humidity and then less and less rapidly with further in- 
crease of relative humidity. But in the region between 50 and 80 
per cent relative humidity a reversal occurs and the moisture con- 
tent mounts at an ever increasing rate as the condition of saturated ~ 
water vapor is approached. At the standard hygrometric condition 
the moisture content is from 5 to 10 per cent of the weight of the 
dry paper, the amount depending upon the kind of paper. Between 
about 35 and 65 per cent relative humidity this moisture content 
difference for different kinds of paper is practically constant, the 
rate of increase of moisture content of most papers being virtually 
constant in this region. 

Weight: The change in the weight of a sheet of paper as a re- 
sult of fluctuations in the hygrometric state is of course the same 
as the change in the moisture content. However, the change in ream 
weight is somewhat different from the change in moisture content, 
owing to the concomitant change in area of the sheet. With in- 
crease in relative humidity the increase in ream weight is slightly 
less than the increase in total weight. With decreasing relative 


HBVGROMETRIC STATE 4] 


humidity the ream weight changes slightly more rapidly than total 
weight. 

Area: ‘The area of a sheet of paper normally increases some- 
what with increasing moisture content. The change is greater in 
the cross direction than in the machine direction since the fibers 
expand in diameter and little or none in length, and the prepon- 
derance of fibers have their diameters in the cross direction. Ac- 
cording to available data, a change of 10 per cent in relative humi- 
-dity from the standard results in a change in dimensions of a stan- 
dard area (area under standard hygrometric state of 65 per cent 
relative humidity and 70 degrees F.) ranging from less than 0.05 
per cent to nearly 0.5 per cent, the amount depending upon the kind 
of paper and the direction of the measurement. 

Tensile Breaking Strength: The breaking strength of paper is 
greatest at about 35 per cent relative humidity, decreasing in a 
regular manner from this point with either increasing or decreasing 
relative humidity. Fluctuations in hygrometric conditions have a 
somewhat greater effect on the breaking strength in the cross di- 
rection than on that in the machine direction. According to avail- 
able data, a change of 10 per cent in relative humidity from the 
standard results in a departure from a standard breaking strength 
(that at standard hygrometric state) of some 5 to 25 per cent, the 
amount depending upon the kind of paper and the direction tested. 

Elongation at Rupture: Elongation at rupture increases with 
increasing relative humidity and the curves for this property are 
somewhat similar in form to those for moisture content. The 
effect is somewhat greater in the machine direction than in the 
cross direction. According to available data, a change of 10 per 
cent in relative humidity from the standard results in a departure 
from the standard elongation (that at standard hygrometric state) 
of some 10 to 125 per cent, the amount depending upon the kind 
of paper and the direction tested. 

Bursting Strength (Mullen): The bursting strength of paper 
is also greatest at about 35 per cent relative humidity and decreases 
both ways from this point in a manner similar to the behavior of 
the breaking strength, except that the magnitude of the change is 
only about half of that for breaking strength. 

Folding Endurance (Schopper): In general the folding endur- 
ance increases rapidly with increase of relative humidity, so much 
so that folding endurance tests have very little significance unless 
carried out under constant hygrometric conditions. The change is 
somewhat more rapid in the machine direction than in the cross 
direction. According to available data, a change of 10 per cent 
in the relative humidity from the standard results in a departure 
from the standard folding endurance (that at standard hygrometric 
state of some 5 to 70 per cent, the amount depending upon the 
‘kind of paper and the direction tested. 


~. 


é. 


ies ( 


h 
Ww 


es tron Values at 
S S 


G urves) 


mpos ite 


0. 


aS 


on of Physical Qua 


Variat: 


er “ee? 


Per Cent--Re vtathe Hamden 
42 


rie. 8. 


ical Prop:rt’es of Paper with Chonges in litmid: v. 


Variation ‘n Phys 


Hy GRhOmethiG slATE 43 


Tearing Resistance (Elmendorf): In general, within the hygro- 
metric range which has been studied, tearing resistance increases 
rather rapidly, with increasing relative humidity. The tearing re- 
sistance of some kinds of paper, however, begins to decrease at 
very high humidities. According to available data, a change of 10 
per cent in relative humidity from the standard results in a de- 
parture from the standard tearing resistance (that at standard hy- 
grometric state) of some 5 to 20 per cent, depending upon the kind 
of paper. 

Permeability: Tests involving the penetration of water and its 
solutions into paper, such as tests for degree of sizing, water re- 
sistance, saturation, etc., are affected to some extent by the initial 
moisture content of the paper. An increase in the initial moisture 
content (with increase of relative humidity) results in an increase 
in the rate of penetration, and a decrease in the total absorption 
(saturation value). 

Fig. 8 shows graphically the extent of the changes in these 
various physical properties of paper from their values at the stan- 
dard hygrometric state. 

d. OrriciAL ConpitionNiInc METHOD 

Following is theofficial Association method of conditioning 
paper for testing: 

I, Relative Humidity and Temperature : 

Whenever required in the test method, the paper sample shall 
he conditioned and tested in an atmosphere maintained at 65 per 
cent relative humidity and 21 degrees C. (70 degrees F.) tem- 
perature. A tolerance of plus or minus 2 per cent in relative 
humidity (63 to 67 per cent) and of plus 5 degrees C. (9 degrees 
F.) in temperature is permissible. 

Il. Conditioning : 

Each specimen of the paper sample, after preparation for ap- 
plication of the test as specified in the test method, shall be 
so suspended that the conditioning atmosphere will have free ac- 
cess to all surfaces. Means shall be provided for so circulating 
the air of the conditioning and testing chamber that its humidity 
and temperature will be uniformly maintained. The conditioning 
time shall be sufficient for the moisture content of the specimen 
to attain equilibrium with the conditioning atmosphere, this to 
be determined by conditioning to constant weight, weighing at 
intervals of not less than % hour. 

Note:—A conditioning period of 2 hours is usually sufficient 
for papers of ordinary weight and composition. - Some papers, 
however, such as boards and certain specialties made water re- 
sistant, may require much longer periods. 

III, Determination of Humidity and Temperature : 

The relative humidity of the conditioning atmosphere shall 

be determined by means of either (1) a sling psychrometer, or 


44 PHYSICAL Ro ae 


(2) a stationary type of psychrometer having the air circulated 
over the thermometer bulbs mechanically. In both cases, the cir- 
culation of air around the thermometer bulbs must be at the rate 
of not less than 3 meters (10 feet) per second. When the sling 
type is used, care must be taken to make the readings as quickly 
as possible after bringing it to rest. 

The thermometers used for determining humidity and tem- 
perature must be accurately calibrated by comparison with certi- 
fied standard thermometers and any corrections found neces- 
sary applied to the readings. 

Note:—It is recommended that thermometers approaching as 
closely as possible to the following specifications be used: Range 
0 degrees C. (32 degrees F.) to 50 degrees C, (122 degrees F.) ; 
graduation, 0.2 degrees. 


2. Machine Direction 


Several methods’ are available for determining the machine 
directions of the original paper sample sheets. The major direc- 
mere inspection of the sheet, as the formation noted on looking 
through it is often conclusive to the trained observer. 

The usual machine wire imparts to the sheet of paper a “wire 
mark” consisting of a series of diamond-shaped marks, the long 
diagonal of which points in the machine direction. If the wire 
mark is sufficiently prominent so that its direction can be de- 
termined this will establish the machine direction. 

Following is the official Association method for determining 
machine direction: 

I. Terminology and Definition: 
The two major directions of paper shall be termed: 

Machine Direction—The direction of paper parallel to its for- 
ward movement on the paper machine. 

Cross Direction—The direction of the paper at right angles to 
the machine direction. 

Il. Specimens: 

The test specimens shail be cut with sides parallel to the major 
directions of the original paper sample sheets. The major direc- 
tions of both the sample sheets and the test speciments shall be so 
marked that they can be respectively identified. For method 1, 
a piece approximately 50 mm. (2 inches) square or a circular 
piece 2 inches in diameter, and for method 2, two strips approxi- 
mately 12.5 mm. (0.5 inch) wide and 152 mm. (6.0 inches) long, 
cut at right angles to each other, shall be used. 

ITI. Methods: 

A positive result obtained by one of the following methods 
shall be regarded as a conclusive aetermination. 

1. Float the specimen on water and note the direction of the 


1 Chemistry of Pulp and Paper Making by Edwin Sutermeister. Chapter 15, 
pages 386-428. 


MACHINE DIRECTION 45 


curl. The axis of the curl is parallel to the machine direction of 
the paper. Paper which absorbs water readily should not be 
exposed to the water for more than a few seconds. 

2. Hold the two strips by the ends in a horizontal position, 
one over the other, placing first one and then the other on top. 
The strip cut in the cross direction will bend the more and fall 
away from the one cut in the machine direction. 

3. Burst the specimen, using the instrument described in the 
official method for determination of bursting strength. The chief 
line of rupture will be at right angles to the machine direction 
of the paper. 

IV. Report: 

In reporting test results the terms “machine direction” and 
“cross direction” shall be used. When the strength of paper in 
the two major directions is reported, it shall be understood that 
the line of bending or rupture of the paper was at right angles to 
the major direction specified. 

V. Additional Information: 

By the term “grain” as applied to paper is meant the machine 

direction of the paper. 


3. Wire or Felt Side? 

In many cases this may be determined very easily by a simple 
inspection but in some papers the wire marks do not stand out 
at all plainly. Sometimes they may be more prominent by plung- 
ing the sample for a moment into water and draining or blotting 
off the excess. The moisture causes the fibers. to expand, thus 
undoing the work of the calenders and restoring the texture of 
the sheet as it left the machine wire. Inspection of a sheet thus 
dampened will often show that the wire marks stand out plainly, 
where before they were indistinguishable. This method very often 
proves satisfactory even for coated paper. 


4. Weight of Paper 
a. OrriciIAL METHOp. 

Following is the official Association method for determination of 
ream weight of paper: 
I. Apparatus : 

The balance used for weighing paper shall have a sensitivity of 
not less than 0.25 per cent of the load applied and shall be so 
graduated that readings of this degree of accuracy can be made. 
The balance shall preferably be a specially constructed sheet 
weighing device indicating the equivalent weight of a 500-sheet 
ream and a 480-sheet ream in pounds when a specimen consisting 
of one sheet of designated size is weighed. The balance musi 
be protected from air currents. 


2 Chemistry of Pulp and Paper Making, by Edwin Sutermeister, Chapter 
15, pages 386-428. 


46 PHYSICAL-TESTING 


The scale used for measuring the size of the specimen shall be 
graduated not more than 0.05 inch (1.27 mm.). 

For trimming the specimens to the desired size, a special paper 
-cutter with an attachment for ensuring parallelism of the opposite 
-cut edges is recommended. 

IT. Calibration: 

The balance shall be calibrated at intervals of not more than 
30 days, both with increasing and decreasing load, by applying 
accurate weights. Care must be taken that, before calibrating, the 
‘balance be properly leveled and give zero reading with no load. 
Ili. Method: 

The specimen for test shall consist whenever possible of at 


Fic. 9a: 
Quadrant Scale. (Fred Baker, New York, N. Y.) 


WEIGHT OF. PAPER 47 


Fic. 9b. 


Torsion Balance. (Torsion Balance Co., New York, N. Y.) 


Teast 10 sheets, 10 by 10 inches (254 mm.) in size, of book or 
writing papers and equivalent amounts of other kinds of paper of 
greater or less weight than these. The specimen shall be condi- 
tioned by the official method, cut accurately as to parallelism of 
opposite edges, its exact dimensions measured to the nearest 0.05 
inch (1.27 mm.), and its weight then determined to the nearest 
0.25 per cent of its total weight, the entire operatron being carried 
out in the official atmospheric conditions. When a balance is 
used which does not indicate the ream weight directly, the weight 
in grams of a single sheet multiplied by 1.102 gives the equivalent 
weight in pounds of a 500 sheet ream for sheets having the size 
of the sheet weighed. Duplicate determinations when calculated 
to ream weight shall agree within 1 per cent of the ream weight. 
IV. Report: 

The report shall give the equivalent ream weight in pounds for 
a ream consisting of 500 sheets, 25 inches (635 mm.) by 40 inches 
(1016 mm.) in size, and also the equivalent weight for the basic 
weight area commonly used by the paper industry for the pat- 
ticular kind of paper. The weight shall be reported to the nearest 
1 per cent of the total ream weight. my 
V. Additional Information : 

To convert the weight of a standard ream of 500 sheets, 25 by 
40 inches in size, to the weight of a ream of 500 sheets of trade 
custom size, multiply the former by one of the factors given 
below: 


PHYSICAL TESTING 


48 


Trade Custom Size 


& © 
Ome 
a 

oS 
~ . 

N 
BAN 
Vv ‘ 
atom 
9 MN 
3 
<4 

sae 

as: 

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a. 
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Beha 
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Ones 
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Boards 


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Cover 


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17 x 22 


oe 


F 


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a 


nF 


ERE 


ays 


sony 


Fic. 9c 


Basis Weight Scale. (Thwing Instrument Co. 


Philadelphia, Pa.) 


WEIGHT OF PAPER 49 


~ ~ 


Fic. 9d. 
Pea and Beam Scale Commonly Used in Paper Machine Rooms. 
(Fairbanks & Co., New York, N, Y 


b. BALANCES AND SCALES 


Various types of weighing devices are illustrated in Figs. 9a 
to 9d, inclusive. 

The sheet-weighing device that indicates the equivalent weight in 
pounds in terms of a 5(00-sheet ream, is most suitable for labora- 
tory or mill use. 

In weighing very small samples it is not desirable to use a weigh- 
ing device graduated in terms of a 500-sheet ream. For such cases 
a chemical balance should be used and the weight in grams multi- 
plied by 1.102 will give the equivalent weight of 500 sheets of the 
size weighed, 


Formula for sample weight on sheet paper scales: 


iwte eine) 5<1_.C1,000) 
—_ — = weight 25 x 40—500 
Area of sheet in sq. in. 


(wt. in lb. & (area of trade size desired) d 
$C 6 = wt, of trade size desired 
Area of sheet in sq. in. 


It is obvious that the samples being weighed must be accurately 
measured to determine their size, and this is done by means of an 
accurate rule, graduated in 0.05 inch. The following formula 
is of assistance where a is scale reading, b is one dimen- 
sion of the sample, c is the dimension at right angles to b, and d 
is the number of paper in the sample: 


50 PHYSICAL ‘TES TING 


a xX 15060 
—_—_—————— = weight in lb. per ream 25 x 40—500 
Or Tex a 

For samples of paper weighing less than 20 pounds on the 
quadrant scale a chemical balance is used. For convenience the 
following formula is used: 


(Weight in grams) X (1,102) x (1,000) 
—- = wt. in lb. per ream 
(Area of samples in sq. in.) X (number of sheets) 25 x 40—500 


To convert the weight of the standard ream to the weight of a 
ream of the desired trade size, it is only necessary to multiply the 
weight of the former by the area of the latter and divide by 
1,000, provided, of course, that the Jatter ream contains 500 sheets. 
3. CONVERSION Factors. 

The weight of a ream folio size, 17 x 22—500, can be stated 
as the substance number. 

A method for determining the substance number on small 
samples by the analytical balance is as follows: A flat piece of 
thin metal cut exactly 2 x 2 1/16 inches is held upon the sample 
and a sharp instrument run around the edge of the metal. The 
sample cut exactly 2 x 2 1/16 inches has a substance number 
equal to its weight in centigrams. 


Weight in centigrams & 500 sheets X 0.374 sq. in. per sheet 


; = substance 
45,360 centigrams per pound X 4.125 sq. in. in sample 


Weight in centigrams X 178,000 


es substance number 
187,110 


TYPICAL EQUIVALENT WEIGHTS IN STANDARD AND 
TRADE SIZES 


Weight of ream Trade size ream Area of sheet Weight of ream 
25 x 40—500 500 sheets trade size 
Ib. in. in. Ib. 
52.6 Zax oe 950.0 50 
64.2 ie ene 374.0 24 
100.0 DO G25 500.0 50 
156.0 22.5 x 28:5 641.3 100 


Conversion between ream basis weight and grams per square 
meter: 


Weight in grams per sq. m. = 


(Weight in lb. of any ream, 500 sheets) XK 1406.13 


—— 


Area of sheet in sq. in, 


Weight in lb. per ream of 500 sheets = 
(Weight in g. per sq. m.) X (Area of sheet in sq. in.) 


1406.13 


To convert to lb. Ream size To convert to grams 
0.267 17 x 33—500 chaps) 
07145) 25 x 40—500 1.40 
0.429 20 x 30—... 2030 
0.591 24 x 36—480 1.69 
0.675 25 x 38—500 1.48 
0.618 24 x 36—500 1.62 


Fic. 10a. 
Mullen Bursting Strength Tester. (B. F. Perkins & Son, Holyoke, Mass.) 


Fic. 10b. 
Cady Bursting Strength Tester. (E. J. Cady & Co., Chicago, Til.) 


51 


4 PHY ShUAT. sis bis 


Length of paper in a roll: 


Roll weight Ream area (sq. in.) 
Length in ft... = ——@@@—@———$— quem x ae 
Ream weight X roll width 12 
Ream size Factor 
17 22500 Fie eb att oa ee 15,583 
25" X'38—-S00Ge i a ee ie ee 38,583 
25K EO —— SOO oa laceahace Chekate eae eke eee 41,667 
20°. 26—=500... A Ae es ee 21,667 
20 X28 SOA BO i Grek sisee Ca oe one nee eee 24,000 
24-3 362-480) 4 25 pS Pee eee eee eae 34,500 


5. Bursting Strength 
a. DESCRIPTION 


There are two types of testers available for determining the 
bursting strength of paper and board. One is of the hydraulic 
type in which the paper is clamped against a rubber diaphragm, 
through which the pressure is applied to a circular area of the 
paper measuring approximately 1 square inch. The pressure is 
indicated on a special Bourdon tube gage. The second type is of 
the spring operated metal plunger design in which the paper 1s 
clamped between annular rings, through which a spring operated 
plunger is forced. 

Although a large amount of data has been collected by indivi- 
dual laboratories with the instruments shown in the accompanying 
photographs (Figs. 10a, 10b, 10c, 10d) very little information has 


Fic. 10c. 
Ashcroft Bursting Strength Tester. (Ashcroft Mfg. Co., New York, N. Y.) 


BURSTING STRENGTH 33 


Fic. 10d. 
Webb Bursting Strength Tester. 


been published. There appears to be very little, if any, relation 
between the data obtained with these three testers. With averages 
of equal number of tests, the variation seems to be inversely pro- 
portional to the diameter of contact. The hydraulic type of burst- 
ing strength tester is illustrated in Figs. 10a and 10b, and the 
plunger type in Figs. 10c and 10d. 


b. OrricraAL AssocriATION METHOD 
This method, which follows, specifies the use of the hydraulic 
type of tester. 


I. Apparatus : 

The testing instrument shall consist of: (1) A circular aperture 
31.5 mm. (1.24 inches) in diameter in a’ plane surface, the aperture 
registering exactly with a similar aperture in a second plane 
surface. One aperture shall communicate with a hydraulic cham- 
ber and the other shall be movable along the axis passing through 


34 MPHYSICAL TESTING 


the centers of the two apertures. (2) Means of firmly clamping 
the two plane surfaces together. The clamping pressure and 
the extent of the contacting plane surfaces shall be such that 
there shall occur no slipping or creeping during the test of a 
specimen clamped between the plane surfaces and no injury to 
the specimen so clamped. (3) A rubber diaphragm firmly se- 
cured to the inner side of the aperture in the hydraulic cham- 
ber so as to close it off and expand through it when hydraulic 
pressure is applied. (4) Means of applying hydraulic pressure 
through a noncompressible fluid to the rubber diaphragm. (5) 
Means of accurately and continuously registering the pressure 
maintained in the hydraulic chamber, the Bourdon tube pressure 
gage being preferred. 

IT. Specimen: 

Specimens for test shall be so selected from a sample secured 
by the official sampling method, as to be representative of the 
sample. 
lil. Method: 

The specimen shall be firmly clamped in position and pressure 
applied within the hydraulic chamber at a uniform rate such that 
the noncompressihle fluid shall be. displaced against the rubber 
diaphragm and through the aperture at a rate of 75 cc. per min- 
ute’ until the paper bursts. The gage used must be such that 
the bursting strength of the paper tested will not be greater than 
3% of its capacity, nor less than 1% of its capacity. The gage read- 
ing shall be recorded to the nearest 2 per cent of the total read- 
ing. At least 10 bursts shall be made, each of a different speci- 
men of the sample and an equal number from each side of the 
specimen. Bursting strength tests shall be made on specimens 
conditioned according to the official methed for conditioning, and 
in the atmospheric conditions therein specified. 

IV. Calthration: 

The instrument shall be calibrated at intervals of not more 
than thirty days. The calibration shall be performed as fol- 
lows: The gage shall be removed and calibrated in a horizon- 
tal position with a deadweight gage tester of the piston type. A 
record shall be kept of any deviations from the indicated read- 
ings and corresponding corrections made in test results secured 
with the gage. The gage shall be replaced and the pressure 
chamber refilled with sufficient glycerine to leave the rubber dia- 
phragm, when placed in position, slightly depressed, taking care 
to eliminate all air bubbles. The rubber diaphragm shall be re- 
newed at least every thirty days. 

V. Report: 

The report shall include the average, the minimum and maxi- 
mum test results. The readings of the gages shall be reported 


3 This rate is equivalent to turning the hand wheel of the ordinary type of 
bursting strength tester at a rate of 120 r.p.m. 


THICKNESS 55 


to the nearest 2 per cent of the total reading and shall be ex- 
pressed as “points.” 
c. RATIO 


The bursting strength test to be of greatest use must be ex- 
pressed in terms of the weight of the sample. This ratio of 
strength to weight may then be directly compared with the 
strength ratio of any other paper. 


The strength ratio may be expressed as a percentage. 
Bursting strength x 100 
Wt. in lb. (on a size 25 x 40—500) 


Strength ratio = 


6. Thickness 


The following is the official Association method of determining 
the thickness of paper: 


I, Apparatus: 

(a) A micrometer of the spring actuated, dial type shall be 
used. The plunger shall be capable of being raised by the appli- 
cation of an upward pressure to it. The plunger surface shall be 
circular in shape and not less than 9.7 mm. (0.38 inch) nor more 
than 16 mm. (0.63 inch) in diameter. The dial shall be graduated 


PGe LE 
Cady Thickness Micrometer. (E. J. Cady & Co., Chicago, III.) 


56 PHYSICAL TESTING 


preferably in divisions indicating a thickness of 0.0127 mm. (0.0005 
inch) and in no case greater than 0.025 mm. (0.001 inch). Gradua- 
tions indicating a thickness of 0.0254 mm. (0.001 inch) shall be 
at least 3 mm. (0.12 inch) apart. Convenient means shall be pro- 
vided for setting the pointer to zero position. 

(b) The surfaces of the plunger and anvil shall be plane and 
parallel to within 0.005 mm. (0.0002 inch). 

(c) Under normal operating conditions the downward pressure 
of the plunger shall be not less than 709 grams (25 ounces) and 
not more than 1418 grams (50 ounces), at a reading of 3.81 mm. 
(0.15 inch). 

(d) Measurements made on standard steel thickness gages shall 


be within the following tolerances. 


Permissible deviation of 
reading from actual 
thickness of standard 
Intervals steel gage 
0 to0:25. mm...(0to’ 0.01 in inch) 5 = a eee 0.0025 mm. (0.0001 in.) 
Over 0.25 mm. to 1.02 mm. (0.01 to 0.04 in.)..... 0.0051 mm. (0.0002 in.) 
Over 1.02 mm. to 3.05 mm. (0.04 to 0.12 in. incl.) 0.0102 mm. (0.0004 in.) 


II. Specimens: 

The test specimens shall consist of original sample sheets so 
selected as to be representative of the entire sample. 
III, Method: 

At least 10 thickness tests shall be made, each on a different 
specimen except in the case of paper less than 0.05 mm. (0.002 
inch) in thickness when a sufficient number of specimens shall be 
placed together and tested so that a reading on the scale of not 
less than 0.13 mm. (0.005 inch) is obtained. Thickness tests shall 
be made on specimens conditioned by the official method and in 
the atmospheric conditions therein specified. 

IV. Calibration: 

(a) For testing for compliance with Section 1 (b), a hard 
steel ball, 4.77 mm. (0.125 inch) in diameter shall be placed at 
different points on the anvil and the thickness readings observed. 
It is recommended that the ball be fixed in a flat piece of metal, 
part of which acts as a handle. 

(b) For testing for compliance with Section 1 (c), the pres- 
sure must be measured by means of a suitable balance device 
applied to the plunger. (Details of such device may be obtained 
from the U. S. Bureau of Standards.) 

V. Report: 

The average, maximum and minimum thickness shall be re- 
ported in parts of an inch to the nearest 0.0025 mm. (0.0001 inch). 
VI. References: 


“A Study of Commercial Dial Micrometers for Measuring the Thickness of 
Paper.”—P. L. Houston and D, R. Miller. Technologic Paper No. 226, 
U. S. Bureau of Standards. 

The type of thickness tester mentioned is shown in Fig. 11. 


7. Bulk 
The bulk of paper is the thickness of a certain number of pages 
and applies more particularly to book papers where the printer - 


BULK “i 


Hig 212: 
Bulk Tester. (B. F. Perkins & Son, Holyoke, Mass.) 


desires a book of a certain number of pages to bulk one inch. 
The bulk of a paper is measured by cutting out short strips of 
paper, piling them up to the required number and measuring the 
combined height of the pack. This measurement may be made by 
the use of a Perkins bulk tester (Fig. 12). This instrument 
measures the bulk in inches; also the pressure of clamping, and 
takes the place of the ordinary graduated sliding clamp which is 
in common use. In specifying the bulk of a paper, where the hand 


58 PHYSICAL  FESTING 


clamp is used, it is necessary to specify whether heavy, medium or 
light pressure is used. In using the Perkins bulk tester, the pres- 
sure is specified in pounds per square inch, as indicated on the dial. 


8. Folding Endurance 

a. GENERAL INFORMATION 

The folding endurance of paper is measured by means of an 
instrument by which the paper is held under a fixed tension and 
repeatedly folded on itself until it breaks. There are two types 
of commercial instruments available. The type specified in the 
official method following is known as the Schopper (Fig. 13), 
which was originally designed by Louis Schopper. This was de- 
signated in the official method owing to its being the only commer- 
cial instrument in extensive use at the time and to very complete 
‘data on its performance being available. The other type of folder 
described appears, in principle, to have several advantages. Refer- 
ence to the discussion of effect of hygrometric state on the folding 
endurance test (page 41) will make clear the necessity of accu- 
rately controlled humidity conditions for this test. 
b. OrricrAL ASSocIATION METHOD 
I. Apparatus: 

The testing instrument shall consist of: 


Miers. 
Schopper Folding Endurance Tester. (Foreign Paper Mills, New York, N. Y.) 


FOLDING ENDURANCE 59 


(1) Two horizontally opposed jaws which are constrained to 
move in the same straight line without rotation. The jaws shall 
be suitably supported as by frictionless rollers (see note). The 
jaws shall be adapted to maintain the ends of the specimen in the 
same vertical plane. There shall be provided a means for holding 
the jaws in a fixed position while inserting the specimen and a 
means of subsequently subjecting the specimen to a maximum 
tension of 1 kilogram and a minimum tension of approximately 
0.8 kilogram alternately as the specimen is folded and unfolded. 

Note—Cylindrical rollers are preferable to the knife-edge rollers 
some times used for the purpose as the edges of the latter fer- 
quently become flattened, causing increased friction and conse- 
quent error in the results. 


(2) A vertically slotted, horizontally reciprocating blade mount- 
ed between the jaws and moving transversely to the line of motion 
of the jaws in such manner that the edges of the slot shall push 
the specimen alternately to either side of its neutral position in_ 
the line of motion of the jaws by a distance of 10.16 mm. (0.400 
inch). The slotted blade shall have a thickness of 0.50 mm. 
(0.020 inch) and the edges of the vertical slot shall be rounded to 
a cylindrical surface. The vertical extension of the slot shall be 
such as to extend beyond the upper and lower edges of the speci- 
men. 


(3) Four rollers rotating on vertical axes mounted in a quad- 
rangle about the central position of the vertical slot in the recip- 
rocating blade so as to cause the specimen to fold around the 
edges of the vertical slot and lie against the blade as it moves 
back and forth. These rollers shall be so mounted that the recip- 
rocating blade bisects the clearance between rollers in one direc- 
tion and the specimen in its neutral position bisects the clear- 
ance between rollers in the transverse direction. The minimum 
clearance between the blade and the rollers on either side shall be 
€.38 mm. (0.015 inch) and the minimum clearance between rollers 
in the space occupied by the specimen shall be approximately 
0.50 mm. (9.020 inch). The design throughout shall be such as 
to entail a minimum of friction in the moving parts. 

(4) A means of imparting harmonic motion of constant period 
to the reciprocating blade. A power driven apparatus is prefer- 
able. 

(5) A device for registering the number of double folds re- 
quired to sever the specimen. 

IT. Specimens: 

Specimens to be tested shall be cut accurately in each principal 
direction of the paper with a width of 15 mm. (0.59 inch) and a 
length such as to insure a firm grip in the jaws without buckling. 
They shall initially be free from foldsi or wrinkles or blemishes 
not inherent in the paper. The edges of the specimens must be 


60 PHYSICAL TESTING 


clean-cut and parallel to the opposite edges. The specimens shall 
be so selected from the sample secured by the official sampling 
method as to be representative of the sample. 

III. Method: 

With the vertical slot of the reciprocating blade in its central 
position the specimen shall be placed in the slot and the ends 
clamped firmly and squarely in the jaws with the surface of the 
specimen lying wholly within one plane. The specimen shall be 
handled by the ends and not touched with the hands in the region 
which is to be folded. The specified tension shall then be applied 
and the specimen folded at a uniform rate of approximately 120 
double folds per minute until it is severed at the crease. The 
number of double folds required to sever the specimen shall be 
recorded. Not fewer than 10 strips cut in each principal direction 
of the paper shall be tested. Folding endurance tests shall be 
made on paper conditioned according to the official method for 
conditioning, and in the atmospheric conditions therein specified 
IV. Calibration: é 

Two pairs of bow dividers, a 1 kilogram weight, and preferably 
a suitable medium, such as a balanced frictionless pulley or bell- 
crank lever, for applying deadweight load to a horizontally mov- 
ing jaw are required for the calibration. . 


All working parts shall be in good condition, well oiled and in 
proper adjustment. Especial attention should be given to the con- 
dition of the supporting rollers, particularly if they are of the 
knife-edge type, replacement being necessary if the edges are worn 
flat at any point. 

The calibration shall be made essentially as follows: 

On each jaw make two very small punch-marks in a line par- 
allel with the direction of motion of the jaw, one punch-mark 
being made on the shoulder of the jaw and the other on the 
adjacent shoulder of the fixed jaw-stem guide. Clamp in the 
jaws, according to procedure under Method, a strip of cellu- 
loid 0.005 inches thick. Revolve the driving wheel until the slot 
in the folding blade is farthest from its central position and then 
apply the tension to the jaws by pulling out the two spring hous- 
ings simultaneously. Adjust one of the bow dividers to accur- 
ately span the interval between the punch-marks on one jaw and 
adjust the other pair of dividers similarly to span the interval 
between punch marks on the other jaw. Take care that these 
divider settings remain unchanged during the calibration. Release 
the spring tension, revolve the driving wheel a half revolution, 
again apply the spring tension and see if the intervals are the 
same as before. If not the crank pin is probably worn and must 
be put in repair so that each interval is the same for the two 
antipodal positions. Apply a deadweight load of 1 kilogram (see 
note) to one of the jaws, tap apparatus lightly and allow the 


FOLDING ENDURANCE 61 


stressed jaw to come to a stable position. Adjust the tension of 
the spring until the interval between the two punch-marks is ex- 
actly the same as for the original setting of the dividers for that 
jaw. In a similar manner adjust the spring tension of the other 
jaw so that a deadweight load of 1 kilogram produces the interval 
between punch-marks for which the other dividers were set. This 
procedure insures that the maximum tension on the specimen being 
folded is exactly 1 kilogram. Put a specimen in place in the tester 
and apply the tension as for a folding test. Turn the driving 
wheel until the folding blade is farthest from its central position 
as at first and see if the two intervals are the same as for the 
setting of the respective dividers. If so the tester is ready for 
use. If one interval is greater and the other less than the setting 
of the respective dividers it is impossible to calibrate the instru- 
ment until the jaw springs have been replaced by matched springs. 
The folding tester shall be calibrated at intervals of not more 
than 30 days. 

Note—The deadweight load may be applied in the horizontal 
normal operating position by means of a balanced bell-crank lever 
having knife edge suspension or by means of a frictionless pulley 


Fic. 14. 


Bell-Crank Lever for Calibrating Schopper Folding Endurance Tester, 
Bureau of Standards, Washington, D. C.) 


62 PHYSICAL TESTING 


over which is passed a strong thread or fine wire, one end of 
which is fastened in the jaw and the other attached to a kilo- 
gram weight. In the latter case it is necessary to take one of 
the jaws with its support out of the way while calibrating the 
other, and to take care that the wire or thread does not touch 
any part of the apparatus other than those specified; or if de- 
sired the jaw to be calibrated may be removed together with 
housing and support, taken apart so as to obtain the weight of 
the jaw, reassembled and clamped in a vertical position, and 
stressed by a deadweight which together with the weight of the 
jaw is equal to 1 kilogram. 

bk Report: 


Tht results shall be reported in double folds. The average, 
the maximum and the minimum folding endurance for both of 
the principal directions of the paper shall be reported. 

VI. References: 


“Folding Endurance of Paper.’—F. P. Veitch, C. F. Sammet and E. O. 
Reed. Paper 20, No. 12 (May 30, 1917). 

“Resistance to Folding.’—W. Herzberg. Chemical Abstracts 14, page 
2262 (July 20, 1920). 

“Calibration and Adjustment of Schopper Folding Tester.”—F. T. Garson 
and L. W. Snyder (describes use of bell-crank lever for calibrating). Bureau 
of Standards Technologic Paper. No. 357. 


c. CALIBRATION 

Following is a description of a bell-crank lever ae at the 
Bureau of Standards for calibrating the Schopper folding tester 
(Fig. 14): 

This device is a convenient means of adjusting the tension on 
the clamp springs without disturbing the assembly of the tester. 
It consists of a bell-crank lever having two arms of equal length 
and at right angles to each other, the intersection being on the 
knife edge K.. The knife edge rests on the end of the bracket 
B which is clamped about the fixed barrel of the spring housing 
in a definite position. The bell-crank lever is counterbalanced so 
that it is in static equilibrium as it rests on the knife edge support, 
the weight W and the tab T being removed. In using the appara- 
tus the proper deflection interval is determined as outlined in 
the calibration method is spanned by the bow divider D. The 
bell-crank lever is then put in place, the tab T is clamped between 
the jaws (the tab T is connected to the lever arm by a short 
link) and a 1-kilogram weight W is suspended from the hook at 
the end of the other arm. The spring is now adjusted until the 
proper deflection interval is obtained as indicated by the setting 
of the dividers D. During this adjustment the spring housing is 
tapped lightly so as to bring the spring to equilibrium. 

d. M.I.T. (MassacHusetts INSTITUTE OF TECHNOLOGY) FOoLDING 
"TESTER 

In this folding tester (Fig. 15) one end of the strip of paper 

to be tested is held in an oscillating clamp each of whose jaws 


FOLDING ENDURANCE 63 


Pres 15; 


M. I. T. Folding Endurance Tester. (Tinius Olsen Testing Machine Co., 
Philadelphia, Pa.) 


is tapered to a rounded edge. These two edges are cylindrical 
surfaces having a diameter of about 0.75 mm. and are very near 
the center of oscillation of the clamp. As the clamp oscillates 
the paper is bent about these rounded edges through an angle of 
135 degrees each side of the vertical. The test strip is held under 
definite tension, the other end being fastened in a clamp which is 
attached to a calibrated spring. A ratchet counter registers the 
number of double folds required to wéaken the strip sufficiently 
to break under the constant spring tension (usually 1 kilogram). 
The relatively few working parts to be driven by the specimen, 


64 PHYSICAL TESTING 


Pre. 16a: 


Schopper Tensile Breaking Strength Tester. (Foreign Paper Mills, 
New York, N. Y.) 
the absence of jar or impact upon the specimen, the constancy 
of the fénsion during a test, the ease with which the spring is 
calibrated and the readiness with which the spring tension may be 
varied to suit the type of paper to be tested are outstanding 
advantages of this type of tester. 


9. Tensile Breaking Strength 
a. DESCRIPTION 
The tensile breaking strength of paper is the load required to 
‘pull a strip apart. Figs. 16a, 16b, 16c and 16d illustrate the com- 
mercial instruments available for applying this test. The first 


Fic. 16b. 
Scott Tensile Breaking Strength Tester. (Henry L. Scott 
Providence, R. I.) 


65 


PHYSICAL TESTING 


Fic. 16c 


Perkins Tensile Breaking Strength Tester. (B. F. Perkins & Son, 
Holyoke, Mass.) 


two are the pendulum type specified in the official Association 
method following, T hey may be obtained both hand driven and 
electrically driven, the latter being preferable. 

b. OrricraL Meruop 


I. Apparatus: 
The instrument shall consist of, (1) two clamps whose centers 


shall be in the same plane parallel with the direction of motion 


TENSILE STRENGTH 67 


Pig. Lod. 


Schopper Tensile Breaking Strength Tester. (Foreign Paper Mills, 
New York, N. Y.) 

of the stressing clamp and so alined that they will hold the test 
specimens wholly in one plane, (2) a pendulum so attached to 
one clamp as to accurately balance the load applied to the test 
specimen, (3) a device attached to the pendulum to indicate on 
a graduated scale the breaking load of the test specimen, (4) a 
scale graduated in weight units (preferably metric) which may 
be read to an accuracy of not less than 0.2 per cent of the total 
reading and (5) a means of moving the stressing clamp at a 
uniform rate. The machine shall preferably be power driven. 
Ti. Specimens: 

Specimens for test shall be cut accurately in each principal 
direction of the paper, not less than 12.7 mm. (0.5 inch) nor 
more than 25.4 mm. (1 inch) wide, and not less than 140 mm: 
(5.5 inches) in length. The edges of the specimens must be clean 
cut and parallel to the opposite edges. The specimens must be 
accurately cut to the predetermined width. They shall be so se- 
lected from the sample secured by the official sampling method as 
to be representative of the sample. 

III. Method: 

The ratio of the clearance distance between jaws to the width 
of the specimen shall be not less than 5:1, nor more than 12:1. 
The test specimen shall be firmly clamped squarely in the jaws 
of the clamps and the stressing jaw then operated at a speed of 
30.5 cm. (12 inches) per minute until the specimen breaks. ‘The 
breaking load shall be recorded to the nearest 2 per cent of tne 
total indicated retading. The tester shall be of such capacity that 
the tensile strength of the paper tested will be not greater than 90 
per cent, nor less than 10 per cent of the capacity of the tester. 
Not less than 10 strips cut in each principal direction of the pa- 
per shall be tested. Ail the readings obtained when the paper 
breaks at or in the jaws shall be rejected. Tensile strength tests 
shall be made on paper conditioned according to the official meth- 
od, and in the atmospheric conditions therein specified. 


68 PHYSICAL TESTING 


IV. Calibration: 

The machine shall be accurately leveled in both of the princi- 
pal directions. The stressing clamp shall be displaced or re- 
moved and accurate weights corresponding to various divisions 
of the scale markings shall be suspended from the pendulum ac- 
tuating clamp. The weights shall be held at the start and re- 
leased slowly so that the pendulum is actuated at a rate similar 
to that specified above and other conditions must simulate the 
paper testing conditions as closely as possible. A record shall be 
made of deviations from the scale readings and corresponding 
corrections shall be made in the test results. The machine shall 
be calibrated at intervals of not more than 30 days. 

7. Report: 

The result shall be reported in kilograms per 15 mm, width to 
the nearest 2 per cent of the total reading. The average, maxi- 
mum and minimum tensile strength for both of the principal di- 
rections of the paper shall be reported. The report shall include 
the width of the specimen in millimeters. 

c. Wet TENSILE STRENGTH 

It is sometimes desired to determine the tensile strength of 
papers when wet, this applying to papers used in that condition 
such as blueprint. The wet tensile strength is determined by 
breaking a strip of paper of a definite width, after it has been 
immersed in water at a constant temperature for a definite period 
of time. The jaws of the clamps should open in front so the 
ends of the wet strips may be inserted without injury, and are 
set at 10 cm. apart, as a short strip of wet paper can be handled 
more easily. The test strips are cut 15 mm. wide and sufficiently 
long to allow for clamping in the machine. Tests are made in both 
the machine and cross direction, running five to each direction. 
The tester is operated at a speed of 12 inches per minute. The 
strips are placed separately in a water bath at 70 degrees F., for 
20 minutes. After the specified time they are removed one at a 
time and tested immediately. To obtain accurate results extreme 
care must be exercised in handling and clamping the wet strips 
to prevent injury to them. The tensile strength tester used for 
this purpose must have a capacity of not more than 5 kilograms. 


10. Tearing Strength 

Following is the official Association method for determining the 
tearing strength of paper. Fig. 17 illustrates the type of instru- 
ment designated in, this method. 

I. Apparatus: 

The testing apparatus shall consist of a stationary jaw, a mov- 
able jaw carried on qa pendulum, a slitting device and a device for 
registering the tearing force. The pendulum shall perferably be 
in the shape of a sector and carry on it’ a scale, the graduation 
of which shall indicate the tearing force, preferably directly in 


TEARING STRENGTH 


Fic. 17. 


Elmendorf Tearing Tester. (Thwing Instrument Co., Philadelphia, Pa.) 


grams, from 0 to 100, laid off on the sector within approximately 
50 degrees of arc. A stop shall be provided for holding the sector 
in its initial displaced position and for releasing it quickly. With 
the pendulum in its initial position ready for a test, the two jaws 
shall be separated by an interval of about 3 mm. (0.12 inch) and 


69 


70 PHYSICAL. TESTING 


shall be in line so that the specimen clamped in them lies in a 
plane perpendicular to the plane of oscillation of the pendulum, 
and so that the tops of the jaws are in a horizontal line. The 
movable jaw shall be so placed on the sector that a line in the 
plane of the sector from the point of suspension of the pendulum 
to a point where the top of the jaw is in contact with the speci- 
men shall be about 10 cm. (4 inches) long and shall make an angle 
of about 30 degrees with the plane of the specimen. The slitting 
device shall be so arranged as to cut an initial slit in the speci- 
men half-way between the two jaws and extending from the 
lower edge of the specimen to a distance of about 4 mm. (0.16 
inch) above the top of the jaws. 

IT. Specimens: ; 

Specimens for test shall be cut accurately in each principal direc- 
tion of the paper not less than 6.3 cm. (2.5 inches) in length (the 
horizontal position when placed in the jaws) and of such width 
that the paper shall extend exactly 43 cm. (1.69 inches) above the 
apex of the initial slit. The edges of the specimens must be clean 
cut and the opposite edges parallel. The specimens shall be sa 
selected from a sample secured by the official method as to be 
representative of it. 

III, Method: 

Enough sheets shall be torn at one time so that the readings on 
the scale shall be not less than 20 grams and not more than 40 
grams. The test specimen shall be so placed in the jaws that it 
rests evenly on their bottom plates and so that the paper extends 
a distance of not less than 2.5 cm. (1 inch) into the movabie 
jaw. Readings obtained when the tear deviates more than 6.3 mm 
(0.25 inch) from the line of the initial slit shall be rejected. 
The sector stop must be released sharply in operating the in- 
strument. The knife for making the initial slit shall be main+ 
tained sharp. Not less than 5 tearing tests shall be made in 
each principal direction of the paper and the results shall be 
computed in grams per single sheet of paper by multiplying the 
readings of the instrument by 16 and dividing by the number of 
sheets tested at one time. Tearing strength tests shall be made 
on paper conditioned by the official method and in the atmos- 
pheric conditions therein specified. 

IV. Calibration: ; 

With the sector raised to its initial position and resting against 
its stop the jaws shall be accurately alined, readjusting the stop if 
necessary. The ball bearings shall be adjusted so as not to bind 
and shall be well oiled. The instrument shall be levelled so that 
the edge of the stop against which the sector rests in its initial 
position lies vertically below the point of suspension of the sector. 
A white line is usually placed on the sector for convenience in 
making this adjustment. With the sector freely suspended and 


TEARING STRENGTH 71 


at rest this mark should be in line with the edge of the stop. Verify 
the position of the mark with a plumb line cutting the axis of 
suspension of the sector. After being levelled, the instrument 
shall be operated several times with nothing in the jaws (movable 
jaw closed) to find if it registers zero with no tearing load. If 
necessary the pointer stop shall be adjusted until the zero read- 
ing is correctly registered. Place the pointer exactly on zero. 
Without again touching the pointer operate the instrument three 
times, being very careful each time not to jar the pointer in setting 
the sector against its stop. The pointer will be pushed beyond 
zero for a distance which measures the maximum pointer friction, 
This should be equivalent to not more than 3 grams (compare with 
distance from zero to 3 on scale). If necessary to reduce this 
friction, clean pointer sleeve and groove (washing with gasoline 
if necessary) and apply fresh oil. 

Note: The friction error allowed has been compensated for at 
its maximum value by the shifting of the pointer stop in adjusting 
the zero reading. 

V. Report: 

- The results shall be reported in grams to the nearest 1 gram. The 
average, maximum and minimum tearing strength for both of the 
principal directions of the paper shall. be reported. The report 
shall include the number of sheets torn at one time. 


Fic. 18. 


Bureau of Standards Modification of the Elmendorf Tearing Tester 
for Increasing Its Capacity. 


72 PHYSICAL TESTING 


VI. References: 

“Tearing Strength Test for Paper.”—-A. Elmendorf, Paper, 26, folio page 
302 (April 21, 1920). 

“ Tearing Strength of Paper, Supplementary Study of Commercial Instru- 
ments of Determining.’”—P. L. Houston, Paper Trade Journal 74, No. 10, 43 
(March 9, 1922). 

A publication of the Bureau of Standards, Means of Increasing 
the Capacity of the Elmendorf Tearing Tester, describes a modifi- 
cation of this tester which makes possible its use for testing very 
strong and heavy papers. This modification is illustrated by 
Fig. 18. The publication also contains additional information 
‘on calibration and adjustment of this instrument. 

It is doubtful if a shearing stress type of tester such as this 
actually gives a test in accordance with service conditions as in 
the latter case the paper tear is usually a combination of shear- 
ing stress and eccentrically applied tensile stress. There is need 
of further investigation in the direction of improving the design 
of tearing instruments. 


11. Wet Rub 


Determination of the resistance of paper, when moistened, to 
surface abrasion is important in the case of most surface treated 
papers such as blueprint, map and ledger. Fig. 19 illustrates an 
instrument developed at the Bureau of Standards for obtaining 
a reproducible numerical value for this property. It consists of 
(1) a means of clamping the specimen over a smooth, hard sur- 
face; (2) a power driven rubber friction surface or mechanical 
finger, maintained under constant pressure; (3) a means of keep- 
ing the paper moistened, while it is being tested; (4) an electrical 


Fic. 19. 
Wet-Rub Tester. (Bureau of Standards, Washington, D. C.) 


WET RUB if: 


Fic. 20a. 
Gurley Densometer. (W. & L. E. Gurley, Troy, N. Y.) 


contact device which automatically stops the tester as soon as a 
hole is worn through the paper; (5) an automatic counter to record 
the number of rubs. 


12. Air Resistance or Porosity 


There are three classes of instruments available for this pur- 
pose: (1) those which compress the air and force it through 


Fic. 20b. 
Schopper Densometer. (Foreign Paper Mills, New York, N. Y.)- | 


74 | rae 


POROSITY 75 


Fic. 20c. 


Emanueii Porosimeter. (Philip Torchio, New York, N. Y.) 


the paper under hydrostatic pressure; (2) those which create a 
partial vacuum and draw the air through the paper; and (3) 
those which measure the pressure drop through the instrument 
caused by the resistance of the paper to permeation of air. In- 
struments of the first class are somewhat more simple and have 
been used more extensively than instruments of the second class, 
even though they are open to the objections that (1) when water 
is used the air is forced through the paper at a higher humidity 
than normal, causing swelling of the fibers which reduces the 


76 PHYSICAL -FEusTING 


penetrability of the paper; and (2) the pressure of the air is 
not uniform throughout the test. The first objection may be 
overcome by using a light lubricating oil instead of water. In- 
struments of the third class avoid the objections mentioned and 
appear to embody the soundest principles in general. 

A discussion of this subject, together with descriptions of 
various instruments, is given in Paper 33, No. 17, page 14 (Feb. 
14, 1924). Information on the construction and use of the Eman- 
ueli Porosimeter was published in Paper Trade Journal 85, No. 
10, page 48 (Sept. 8, 1927). The three classes are illustrated, 
respectively, by Figs. 20a, 20b and 20c. 


13. Degree of Sizing 


a. DEGREE OF INTERNAL SIZING 

Paper is made moderately resistant to water by incorporating 
in it a water resistant material such as rosin. A very complete 
discussion of the various methods for measuring the degree of 
sizing of such papers is contained in the Bureau of Standards 
Technologic Paper No. 326, Measurement of the Degree of Sizing 
of Paper, by F. T. Carson. Following are descriptions of the five 
outstanding methods and the conclusions regarding them, ab- 
stracted from this publication: 

Ink Flotation Test: 

A sizing test somewhat similar to the method of Klemm (per- 
haps an adaptation of it) has long been used in this country and 
today enjoys the prestige of custom and precedent. Specimens 
of paper are Hoated on the surface of ink and kept continuously 
under observation until transudation of ink is detected on the 
upper side. The time interval required for the staining through 
of the ink is considered a measure of the degree of sizing of 
the paper. 

Method of Stockigt: 

A specimen of paper is floated on a 2 per cent solution of 
ammonium thiocyanate. The upper surface is lightly dabbed with 
a brush wetted with a 1 per cent solution of ferric chloride until 
red specks of iron thiocyanate appear all over the surface of the 
sheet. The experimental datum of the test is the time from the 
contact of the paper with the ammonium thiocyanate until the ap- 
pearance of the red specks on the upper surface. A useful modi- 
fication of this method consists in applying the ferric chloride at 
frequent intervals with a pen or fine-tipped brush, always in a 
new place, until the red coloration develops immediately. 

Method of Okell: 

An old idea was given a new application when the Kohlrausch 
method of conductivity measurement was cleverly adapted to the 
problem of measurement of the degree of sizing of paper. Ac- 


DEGREE OF SIZING 77 


cording to the proposal of Okell, the paper to be tested is inter- 
posed between the electrodes of a specially constructed electrolytic 
cell having controlled means of bringing the electrolyte into con- 
tact with the paper. As the solution of electrolyte penetrates 
the paper partition from both sides the decreasing resistance 
(or increasing conductance) is measured by means of a Wheat- 
stone bridge. By plotting the resistance (or conductance) against 
time a continuous record is obtained, and, assuming the rate of 
increase of conductance to be proportional to the rate of increase 
of permeation, the data are interpreted in terms of degree of 
sizing. 


ita oe 


Vailey Size Tester. (Valley Iron Works, Appleton, Wis.) 


78 PHYSICAL..TESTING 


Method of Boon and Fourness: 


In order to obviate the use of a sensitive galvanometer or tele- 
phone receiver, the method of Okell is modified so as to substitute 
a series circuit containing a milliammeter for the Wheatstone 
Bridge. A constant temperature is maintained thermostatically. 
An arbitrary end point is chosen ‘which is four-fifths the normal 
conductance of the circuit when operated with no paper in the 
cell. A commercial instrument of this type is illustrated by 
Fig. 21. 

Curl Methed: 


When a small piece of paper is floated on water, it curls up as 
a result of the wetting and consequent expansion of the under 
side. In a short time it attains a maximum degree of curling 
and then begins to uncurl as a result of expansion setting in on 
the upper side of the sheet as the water penetrates beyond the 
median plare. The time from the contact of the paper with the 
water until the instant when the specimen begins to uncurl is con- 
sidered a measure of the relative degree of sizing within the 
sheet for papers of the same thickness, tested under the same 
conditions of temperature and relative humidity. When it is 


Pigs oz, 
Curl Sizing Tester. (Bureau of Standards, Washington, D. C.) 


DEGREE OF SIZING 79 


necessary to test papers of different thicknesses the quotient ob- 
tained by dividing the time by the square of the thickness in each 
case is an expression of the relative degree of sizing within the 
sheet. 

The test is made preferably with an apparatus such as that 
shown in Fig. 22 devised by F. T. Carson, the originator of 
the method. The specimen $ is held in a definite position on a 
float having an.aperture through which the water presents a small 
restricted surface convex upward. The part of the specimen lying 
over this aperture is wetted on the under side. The pointed part 
remains dry and serves as a pointer to magnify the movement due 
to the curling. This pointer is viewed against a background of 
small black dots on a white field, which facilitates determining the 
instant at which it begins to retreat. The whole mechanism is 
controlled by an operating lever, the initial depression of which 
brings the specimen in contact with the water and starts a stop 
watch. A second depression of the lever at the instant the speci- 
men starts to uncurl arrests the stop watch. The time is rec- 
orded. On raising the lever to the vertical position the stop watch 
is set to zero, the transparent hood is thrown back, and the speci- 
mynen is lifted from the water. When a new specimen is put in 
position on the float, all is in readiness for another test. 

Bureau of Standards Dry-Indicator Method: 

The accidental observation that grains of sugar on the surface 
of paper give an indication of the presence of transuded moisture 
by melting down into droplets long before the presence of water 
can be detected by other simple means has led to the development 
of a new method at the Bureau of Standards. Sugar, at first 
used alone, was supplemented to great advantage by adding small 
amounts of dyes. Powdered sugar and one or more water-soluble 
dyes are mixed in such proportion (approximately 50 parts of 
sugar to 1 part of dye) that the mixture shows very little color. 
The mixture is applied through a sieve to the paper being tested. 
The specimen is then floated on a vessel of water at a definite 
temperature and the time determined until the characteristic color 
of the dye begins to appear in the mixture as a result of wetting by 
transuded moisture. This time interval is then interpreted in the 
same manner as in the curl method, either as a measure of the 
relative degree of sizing of papers of the same thickness or by ac- 
counting for the effect of thickness in the manner described under 
the description of the curl method. 

This method is susceptible of a number of modifications. At 
first methyl blue was employed as the dye constituent. Later 
fuchsine, methyl green, and a soluble yellow were used in three 
separate mixtures for the sake of the color contrast which helps 
in determining the end point. A procedure which gives excellent 
results is the following: . 


SO PHYSICAL TESS iis 


Three mixtures are prepared of powdered sugar and small 
amounts of finely divided dyes in the approximate ratio 50:1. The 
first contains methyl green, the second pontacyl scarlet, and the 
third national wool yellow. Three other mixtures are made, using 
pigments insoluble in water instead of the dyes, each of the latter 
three mixtures being made up to match in color one of the first 
three. A fluted sieve (Fig. 23a) is.made of wire screen (about 80 
mesh) such as that used on a fourdrinier paper machine. The 
manner of construction is illustrated by b of Fig. 23. Into 
every other trough one of the sugar-dye mixtures is placed. Each 
sugar-pigment mixture is thea placed in one of the three remain- 
ing troughs, so that it is adjacent to the sugar-dye mixture of the 
same color. A test specimen is cut about 3 inches square and the 
edges folded over to prevent curling. The sieve is dropped on this 
specimen from a height of about a quarter of an inch, as a result 
of which the indicator mixtures are laid down close to one another 
in parallel lines. On floating the specimen, water penetrates 
through and is taken up by the sugar and transferred to the par- 
ticles of dye scattered through it. The colors deepen markedly and 
rapidly and, in contrast with the reference mixtures, stand out 
prominently. The end point is when one is certain that the colors 
have begun to develop. The end point is influenced somewhat by 
the solubility of the dyes. When not in use, the indicator mix- 
tures should be kept in a desiccator. It is well to prepare fresh 
mixtures frequently. In order to get comparative results over a 
period of time, all tests should be made under the same conditions 
of temperature and relative humidity. 

The procedure which, perhaps, best combines simplicity with a 
sharp end point employs one of the sugar-dye mixtures flanked 
on either side by its reference mixtures of sugar and an insoluble 
pigment. In this case only one trough in the sieve is- required. 
This procedure is illustrated by c of Fig. 23. 

The factors necessary for securing accurate results with this 
method are (1) uniform temperature of water and (2) a definitely 
standardized indicator mixture. Extreme atmospheric conditions 


Fic. 23. 
Dry-Indicator Sizing Test Method. (Bureau of Standards.) 


WATER RESISTANCE 8] 


should be avoided. It is desirable to make the tests under ac- 
curately controlled humidity conditions. 

From results of experimental comparison of these methods it 
was concluded that: 

(a) The most probable relative degrees of internal sizing of the 
various samples are best represented by the data of the Bureau of 
Standards dry-indicator method. 

(b) The agreement of the curl method with the dry-ind‘cator 
method is, with a few exceptions, very good. 

(c) The Stockigt method gives fairly consistent results but is 
characterized by an error which increases with iticrease of degree 
of sizing, the error being due presumably to the influence of selec- 
tive adsorption. . 

(d) The data obtained with the electrolytic method are, in 
general, too erratic and inconsistent to be of much value in ap- 
praising paper for degree of sizing. In some cases this method 
agrees satisfactorily with the methods which measure the rate of 
penetration of water, but the degrce of concordance does not 
follow any clearly defined principle, and hence the method can not 
be depended upon for consistent results. 

(e) The ink flotation test is too erratic and fruitless of useful 
information to be considered seriously as a test of the degree of 
internal sizing of well sized papers. 


b. DEGREE oF SURFACE SIZING 


The chief significance of degree of surface sizing is in relation 
to writing inks. ‘The suitability of paper for writing must be 
determined by observation of ink lines and characters on the sur- 
face. No method has come into use for expressing this property 
numerically. Methods which measure the rate of penetration of 
aqueous solutions into and through paper are not valid for this pur- 
pose despite the fact that most of them were proposed with the 
idea of expressing writing quality numerically. An adequate method 
giving a numerical expression for degree of surface sizing and ap- 
plicable to various inks is needed in the interest of research in siz- 
ing and in the preparation of specifications of writing papers if not 
for practical tests. The literature affords no better treatment of 
testing paper with ink than Herzberg’s papier-prufung. 


14. Water Resistance - 


a. DEFINITION 

Water resistance may be considered to be a special case of de- 
gree of sizing in which the liquid involved in the test is definitely 
specified and the time of transudation is a sufficient test. However, 
the terms water resistance and waterproof usually imply a much 
longer time of transudation than is involved in testing degree of 
sizing. 


&2 PHYSICAL TESTING 


b. BurREAU OF STANDARDS GROUND GLAss MeETHop 

The application of this method is illustrated in Fig, 24. The 
chief source of error in testing paper for water resistance has 
seen the untrustworthiness of the means of detecting transuded 
moisture. This source of error has been removed by the use ot 
a ground glass surface in contact with the paper, the ground 
surface absorbing the transuded moisture and revealing it as a 
fugitive dark patch when the specimen is lifted. A shallow flat- 
bottomed vessel, such as the inverted cover of a can, containing 
sufficient paraffin to be about an eighth of an inch deep when 
melted is heated until the paraffin begins to “smoke.” The heating 
is discontinued and the end of a glass cylinder is placed in the 
paraffin. It is allowed to remain for a few seconds until the 
melted paraffin is seen to be mounting up the sides of the cylinder. 
it is then removed, allowed to drain for an instant, and applied 
to the test specimen which has been laid on a smooth surface, such 
as a pane of glass. A weight is then placed on the cylinder and 
allowed to remain until the paraffin has hardened. Such a seal 
will hold more than a foot of water if necessary. A piece of 
ground glass, G, (Fig. 24) is laid on a piece of black paper B, or 
other dark surface, the ground surface of the glass being upper- 
miost. The specimen, P, sealed to the cylinder, C, is placed on the 
ground surface. An inch or two of water is poured into the 


Fic. 24. 
Ground Glass Water Resistance Test Method. 


WATER RESISTANCE 83 


Pic. 252: 


External View of Apparatus, Harvey Water Resistance Test Method. 
(A. R. Harvey, Middletown, Ohio.) 


cylinder. The capillary pressure in pores as small as those in pa- 
per is so great as compared with the hydrostatic pressure that the 
head is immaterial so long as it is small. At intervals the cylinder 
is lifted and any transuded moisture will show as a dark fugitive 
patch on the ground surface. While all the tests of this nature 
are rather sensitive to differences in temperature, the ground glass 
method is particularly so, not only because of the change in viscos- 
ity of the liquid, but also because of the effect of temperature on 
the sensitivity of the ground glass surface. The moisture is re- 
tained by adsorption and adsorption is increased as the temperature 
falls. For this reason it seems desirable to keep the ground glass 
al as low a temperature as is convenient. 


c. MetuHop or A. R. HARvey 

This test is applied where it is desired to find the degree to 
which a board will resist the penetration of moisture. The test 
was developed primarily to be used in connection with an asphalt 
filled board and its relation to sizing or waterproof tests has not 
yet been determined. The method consists in interposing the 
sample under test between a moist and a dry atmosphere, the 
amount of moisture passing through the sample being found by 
weight. The test is influenced by a number of factors, some of 
which are: 


Temperature and humidity of moist atmosphere. 

Temperature and humidity of dry atmosphere. 

Air circulation in moist atmosphere. 

Air circulation in dry atmosphere. 

The apparatus (Figs. 25a and 25b) used consists of a circular 
revolving tray which carries the samples under test and also a 


84 PHYSICAL TIESTING 


Fig. 25i: 
Apparatus With Cover Raised. Harvey Water Resistance Test Method. 
(A: R. Harvey, Middletown, Ohio.) 
drying agent. The whole is encased in an air-tight chamber sur- 
rounded by a thermostatically controlled water bath. The tray has 
a diameter of 21 inches and revolves at a speed of 17.5 r.p.m. 
Small metallic vanes (see Fig. 25c) are fastened to the top of the 
chamber to aid in uniform air circulation. Fight samples are 
evenly spaced around the outer edge of the tray and are prepared 
as described helow. The sample of board to be tested, having 
an area of 33 square inches, is sealed around a triangular frame 
of light tin (see Fig. 25d). The box thus formed contains on its 
bottom a piece of felt saturated with water. The water is intro- 
duced through a hole in the tcp after the box has been completely 
made up in order to avoid wetting the board at any point while 


BicyZ se; 


Internal View Showing Test Samples and Vanes for Air Circulation. Harvey 
Water Resistance Test Method. (A. R. Harvey, Middletown, Ohio.) 


GREASE RESISTANCE 85 


Fics 25d, 


Construction of Test Samples, Harvey Water Resistance Test Method. 
(A. R. Harvey, Middletown, Ohio.) 


sealing. The temperature in the desiccator is brought to 77 degrees 
F., and the samples are placed on the tray and allowed to season 
for l¢hour before making the first weighing. After running for 
a period of 2% to 5 hours the samples are again weighed and the 
loss of water determined by difference. 

15. Grease Resistance 

The principal difficulty in the technique of testing greaseproofed 
paper has been the lack of a satisfactory means of applying the oil 
or other organic liquids to the paper. Such liquids, owing to their 
low surface tension, quickly spread out into a thin film, often 
running over the edges of the specimen and leaving insufficient 
liquid in place to give an adequate test. Similarly, if the speci- 
men is floated the liquid runs over the edges and covers the upper 
surface in a short time. Even when the specimen is formed into 
a receptacle having high walls the organic liquid rapidly creeps 
up the sides, over the top and down inside. Altogether such a 
test is vexatious and unsatisfactory. 

The difficulties have been overcome and the test greatly facili- 
tated in a method developed by Carson at the Bureau of Stand- 
ards. The technique is similar to that of testing water resistance 
by the ground glass method. ‘The test specimen is sealed to the 
end of a glass cylinder with a substance which is not readily 
wetted by organic liquids. A very thick, viscous sirup is most 
satisfactory for the purpose. Glue will serve as well when the 
sirup is not at hand. The specimen is sealed to the cylinder in 
much the same manner as that described above in connection with 
the test for water resistance. The end of the cylinder is touched 
to the surface of the sirup and then applied to the test specimen. 
A seal made in this manner will withstand organic liquids in- 
definitely. 

The actual test may be carried out in several ways. An oil- 
soluble dye may be dissolved in turpentine or oil which is then 
poured into the cylinder, the specimen being placed on a piece of 
white paper and lifted periodically to observe any spots, in the 


86 PHYSIGALZTESTING 


manner recommended by Smith.’ In this case it is an advantage to 
cut a strip a few inches long from the sample to be tested. The 
cylinder is sealed to one end of the strip. with sirup (or glue) and a 
weight is placed on the other end. By this means the specimen is 
always replaced in exactly the same position after being lifted to 
observe the white paper underneath. In testing with turpentine or 
other volatile organic liquids it is preferable instead of using white 
paper underneath the specimen to use a ground glass surface as in 
the test for water resistance. 


A better method is to reverse the process and set the specimen 
which has been sealed to the cylinder, in a shallow glass vessel 
containing the organic liquid, in order that the specimen may be 
viewed from above. This method is illustrated in Fig. 26. A 
piece of heavy cardboard, B, having a hole, H, in the middle is 
supported on a ring-stand. ‘The crystallizing dish, D, containing 
the organic liquid is placed over the hole. The test specimen, P, 
sealed to the cylinder, C, is placed in the organic liquid in the 
crystallizing dish. A rotating mirror, M, pivoted at O, is mounted 
directly underneath the hole, H. The test is carried out near a 
window or a good artificial light giving satisfactory illumination of 
both the mirror and the upper surface of the specimen. The or- 
ganic liquid penetrating through the sheet becomes visible alter- 
nately as light and dark spots as the mirror is oscillated. The ex- 
perimental datum is the time interval until transudation is noted. 


4“The Turpentine Penetration Test for Greaseproof Papers.’’—Technical 
Association Papers, Series VII, No. 1 (June, 1924). 


J eee 
VILL nc ae My enn LLL IL IL LLL EL DED LED IEE OF 


A 


Fic. 26. 


Apparatus for Grease Resistance Test. (Bureau of Standards.) 


Fic. 27. 


The Penescope. An Apparatus for Testing Resistance to Liquids. 
(Thwing Instrument Co., Philadelphia, Pa.) 


87 ; 


ByG; 26a, 


Absorption Test, Klemm Method. An Apparatus Devised by the Bureau of 
Standards for Simultaneous Tests of Several Specimens. 


THE PENESCOPE 89 


16. The Penescope 


An instrument, devised by Allen Abrams for applying penetration 
tests, such as those described above for degree of sizing, water 
resistance and grease resistance, is shown in Fig, 27. It has the 
advantage of permitting continuous observation of the effect of 
the test liquid on the paper specimen. 

The apparatus consists of a cast brass chamber. which is to be 
filled with the testing liquid and the outer rim of which has a plane, 
machined surface; the hollow screw cap in which the test specimen 
is inserted, with a plane, machined surface inside; and the open- 
ings above and below, threaded for % inch pipe connections by 
means of which the testing liquid is introduced, removed, and 
maintained at a desired level, 


17. Absorption 
a. STRIP° | 
The absorption of a blotting paper is indicated by the height 

in millimeters to which, in a given time, a liquid will rise by 

capillary action, when one end of a strip of paper held vertically 
is immersed in water. The height in millimeters to which the 

liquid (preferably water) will rise in 10 minutes is taken as a 

measure of the relative absorption of the paper. 

In making this test, using the “strip” method (Fig. 28a), a strip 
of blotting paper 15 mm. (about 3/5 inch) wide and 150 mm. 
(about 6 inches) long is suspended so that the lower end dips 
3 mm. (about % inch) into a pan of distilled water. Beside the 
strip is a scale reading in millimeters (fractions of an inch), and at 
the end of each minute, for 10 minutes, readings are taken of the 
height to which the liquid rises in the strip. Five tests are made 
in both the “machine” and “cross” direction and an average ob- 
tained. The result is reported as the height to which the liquid will 
rise in 10 minutes. When necessary or advisable the same strips 
may be subjected repeatedly to the test, which will indicate the 

decreasing ability to absorb water or ink. A standard ink of the 
~ tollowing formula may be used: 


FORMULA FOR UNITED STATES GOVERNMENT STANDARD 
WRITING INK 


Grams 
Thana gyes cayeyel Se Mey Tt ec ra A rn SO Al Mere eee A aera ee Uae 23.4 
(CSE, Grecia? a, Se es sae i ea a = a ee om ere ies MED aoe nee ee Iara eed caeae © TF 
HEGEGaTS AS DAC CCT YStAlS "le wee scapes o-sick meet Meche Scie ve Welles lajle ech apens aie cot 30.0 
Dilaiestyarochloric. acid (10 per cent solution) 25.2. see i.e ne 25.0 
Fiano) ME RPM AD NAG orb aaa One Gh Te ee om da ine aa ERICA Tal Rs ecempnicr aC cores 1 
Blue dye (Soluble Blue ‘‘A’”’) color index No. 707 or Schultz No. 539 3.5 


Water to make a volume of 1,000 cc. at 20 degrees C. 


All chemicals used should be of C. P. or U. S. P. quality. 
Particular attention should be given to the blue dye as many of 
these dyes react with phenol and cause a metallic-appearing film 


5 Handbuch der Papierkunde Trea of Paper Technology), by Paul 
Klemm, pages 248-327. 


90 PHY¥SICAL ‘TESTING 


on the surface of the ink. Samples of dyes submitted should be 
tested, and only those dyes which do not react with phenol should 
be used for making this ink. Only distilled water should be used 

This ink should be made in the following manner: Dissolve the 
ferrous sulphate in cold water and add the hydrochloric acid. To 
this add the tannic and gallic acids, previously dissolved in warm 
water. Then add the dye dissolved in warm water and also the 
phenol. Dilute the mixture with water to make a volume of 
1,000 cc. at 20 degrees C. 


b. Pipette ° 

In this test a 1 cc. pipette is used and is suspended in such a way 
that the end of the pipette is % inch from the surface of the test 
sample of blotter. The test sample cui’ 4 inches square is laid felt 
side up upon a coarse wire screen which is supported by a large 
beaker. This is done to prevent as far as possible the blotting 
paper from caving in at the center where the liquid fell upon it. 
(The felt side of paper is the top side of the paper as it leaves 
the paper machine wire.) Both distilled water and the afore- 
mentioned government standard ink are used at the three tempera- 
tures of 60, 70 and 80 degrees F. 


A stop watch is used to measure the time it took the 1 cc. of 
liquid to leave the pipette until it is totally absorbed by the paper. 
Also the diameter of the circular spot on the paper is measured 
immediately at the completion of the time reading. 


c. ToTaL AxpsorPTIon | 

By means of this test, test samples cut 2 inches square are 
first weighed on a chemical balance and then dropped with the felt 
side down on a trough of- distilled water and also on trough of gov- 
ernment standard ink. The same temperatures are used for the ink 
and water as in previous absorbency tests. After a 10 minute 
period of absorption the samples are taken out, drained % minute 
and again weighed to determine the amount of liquid absorbed. 


d. Brotrinc Test’ 


In this test small strips of blotting paper cut % inch wide by 4 
inches long are used to blot signatures that are written with a 
stub pen on ordinary bond paper. The same signature is used 
throughout the test and only one signature is blotted at a time. 
The small size of the test sample causes each blot to be made on 
almost the identical spot in the blotting paper. Government stand- 
ard ink is used as in previous tests and a record is kept of the 
number of times each test sample will blot the signature before 
the ink shows signs of spreading on the paper. The felt side of 
both blotting and bond paper is used throughout the tests, and an 

6 “Absorbency of Paper.’”—E. QO. Reed. Paper) 2a. 19, page 14 (Jan. 
16, 1918); Journal of Indus. & Eng. Chem., Vol. 10, 44 (Jan., 1918). 


7“Testing of Blotting Paper.’-—P. L. Houston and R. H. Ledig. Paper 
Trade Journal 73, No. 19, page 88 (Nov. 10, 1921). 


ABSORPTION 91 


average of three tests is taken as a final result for each blotting 
paper. 

Another method for testing the quality of blotting papers has 
been devised by Dalen. An instrument made by Schopper to 
apply this method is illustrated in Fig. 28b. A definite quantity of 
ink, generally one drop, is allowed to fall from a burette on to a 
strip of well sized writing paper. A strip of blotting paper of the 
same width is brought into contact with the strip of writing paper 
under strictly regulated conditions and the two strips are passed 
together through small rollers driven by a motor. The result is 
the formation of a long or short smudge forming a tail to the 
drop of ink. The length of the smudge depends entirely upon the 
quality of the blotting paper. With papers of poor quality the 
smudge is naturally a long one while with papers of good quality 


Fic. 28b. 
Dalen Blotting Paper Tester. (Foreign Paper Mills, New York, N. Y.) 


92 PHYSICAL TESTING 


Fic. 29. 


Opacity Tester. (Bureau of Standards.) 


the absorption is so rapid that there is not sufficient ink left to 
form an appreciable smudge. 
18. Opacity 

Following is the tentative official Association method for de- 
termining the opacity of paper. The Bureau of Standards opacity 
apparatus designed to apply this method is illustrated by Fig. 29. 
I. Apparatus: 

The essential principle of the contrast method of determining the 
opacity of the paper, herein specified, is as follows. When trans- 
lucent paper is placed over a white surface, the luminosity ob- 
served is composed of the light reflected from the surface of the 
paper plus that which is reflected from the white surface under- 
neath. When paper is placed on a perfectly black surface the 
luminosity is that of the light reflected from the surface of the 
paper only, as the transmitted light has been absorbed. The ratio 
between these two luminosities, termed contrast ratio, represents 
therefore the opacity of the paper, this being unity for perfectly 
opaque paper and zero for perfectly transparent paper. The ap- 
paratus shall consist of a light chamber, a photometer, a standard 
white surface, a standard black surface, and a test specimen 
holder. A particular design of light chamber or box is not es- 
sential. It is essential that the light box be so designed that the 


OPACITY 93 


surface of the sample to be tested shall be illuminated by diffused 
light from all directions above, and that the illumination over the 
black hole and white standard surface be equal. The apparatus 
must be so designed that only the light reflected from the surfaces 
of the paper covering the black and white standards can enter 
the photometer. The white standard surface must not touch the 
surface of the test specimen but must be so near it that a further 
decrease in distance will not affect the test results. (In the 
instrument mentioned below less than 2 mm. was found suitable). 
The white standard shall consist of a block of chemically pure 
magnesium carbonate of high reflecting power. The surface used 
shall be smooth and plane, and shall be covered with a thin (1 mm. 
or less thick), clear (free from color) glass disk. The black 
standard shall consist of a box or cavity of such depth and lined 
with such material that all light entering the cavity will be ab- 
sorbed. The box may be lined with black plush, or smoked with 
acetylene or other soot. A specified make or design of photo- 
meter is not essential. Both halves of the photometric field shall 
be perfectly uniform in brightness over their entire surfaces, and, 
when matched, the dividing line shall disappear along its entire 
length simultaneously. The specimen holder shall be so con- 
structed that the sample is held perfectly flat; otherwise the photo- 
metric field will not be uniform and the precision of setting will 
be poor. A suitable type of apparatus is described in the Bureau 
of Standards publication mentioned. (See VJ.) 

IT, Calibration: 

The requirement that the black and white areas must receive 
equal illumination is tested as follows: 

Both areas are covered with a uniform opaque, mat, white pa- 
per. The photometer is turned so that one half of the field is 
illuminated by light from the part of the paper over the black 
standard, while the other half is illuminated by the light from the 
part over the white standard. The two halves of the photometric 
field are then matched. The whole photometer is then rotated 
about its optic axis through 180 degrees. If the two halves of 
the field are still matched, the condition of equal illumination 
is satisfied. 

Specimens for test shall consist of not. less than three pieces of 
paper so selected as to be representative of a test sample secured 
by the official sampling method, and shall be of sufficient size to fit 
the sample holder and completely cover the standard test surfaces. 
They shall be kept perfectly clean and free from folds and 
wrinkles; and the areas to be tested should not Se touched with 
the fingers. 

IV. Method: 

Not less than three representative test specimens shall be tested 

in the following manner; one of the test specimens shall be placed 


94 PHYSICAL TESTING 


in the specimen holder which shall then be placed in posi- 
tion in the apparatus so that the test specimen covers the 
black and the white standard test areas. The observer shall then 
match for brightness the two halves of the photometric field, using 
the scale interval between 0 and 45 degrees. A second or check 
observation shall then be made, and the two observations recorded. 
The whole photometer shall now be rotated through 180 degrees, 
and two more observations shall be made as before, using the 
scale interval between 45 and 90 degrees. After these four ob- 
servations have been made and recorded, the test specimen shall 
be removed and a second specimen shall be placed in position, and 
four more observations made and recorded as before. The second 
specimen shall then be removed and a third substituted and tested 
as before. The twelve readings shall be recorded and computed 
as in the following example. The readings for the three speci- 
mens are in consecutive numerical order, Nos. 1 to 4, inclusive, be- 
ing for one specimen, Nos. 5 to 8 for another, and 9 to 12 for 
the third, 


Ai Aa 

1 34.6° 3 554°. 

2 34.8 4 oe, 

5 34.5 7 55.4 

6 34.6 8 55.0 

9 34.4 11 55.6 

10 34.5 2 55.4 
Means 34°—34’ 55°—25’ 


tan Ai = .6890, cot Ae = .6894 
Contrast ratio = tan Ai & cot As = 475 


V. Report: 


The results shall be reported in terms of “contrast ratio” to the 
third decimal place. 


VI. Additional Information: 


A Measurement of the Translucency of Paper, U. S. Dept. of Agricul- 
ture, Bureau of Chemistry Circular No. 96; Paper 7, No. 7, 22 (May 1, 
1912). 


Specification of the Transparency of Paper and Tracing Cloth, Bureau 
of Standards Circular No. 63. [Copies of these publications may be obtained 
from the Superintendent of Documents, Government Printing Office, Wash- 
ington, D. C., at 5 cents (cash) per copy.] 


19. Gloss 


Determination of the gloss of paper is one means of measuring 
its degree of finish. The Ingersoll Glarimeter (Fig. 30), which ap- 
pears to be the most suitable instrument available at present for 
measuring gloss, does not take into account the surface texture 
of paper which is a factor as regards printing. A means of meas- 
uring the surface texture is given in the following section. For 
complete measurement of finish of paper it is recommended that 
both gloss and surface texture measurement be made. The ten- 
tative official Association method for measuring gloss follows: 


GEOSS 95 


Fic. 30. 
Ingersoll Glarimeter. (Central Scientific Co., Chicago, IIl.) 


I. Apparatus: 


The testing instrument shall consist of (1) a photometer so fixed 
in relation to the test specimen that the amount of polarized light 
reflected from the test specimen relative to the total amount re- 
flected from the test specimen at an angle of 5714 degrees may be 
measured; (2) a source of diffused illumination consisting of a 
frosted B lamp, G 18% bulb, 110 volts, 25 watts, so fixed in rela- 
tion to the test specimen that the light subtends an angle of 114% 
degrees and falls on the test specimen at an angle of 57% degrees; 
(3) an opal glass diffusing screen between the source of light and 
the specimen aperture; (4) a metal box having the photometer 
housed in one end, the source of illumination housed in the other 
end, and an aperture in one side over which the specimen 1s 
clamped in a fixed position, so made as to exclude all outside 
light and having its interior blackened. 

IT. Specimens: 

The specimens for test shall consist of not less than five pieces 
of paper cut from different portions of the test sample, secured 
by the official sampling method so as to be representative of it. 
These shall be of sufficient size to extend beyond all sides of the 
aperture of the metal box. The test specimens shall be clean, 
free from wrinkles and folds, shall not be exposed for any con- 
siderable length of time to extreme atmospheric conditions, and 
the parts of them actually tested shall not have been touched with 
the fingers. 


96 PHYSICAL PEs Lips 


III. Method: 

The test specimen shall be firmly clamped in position so that-its 
sides extend beyond all sides of the aperture of the metal box. 
If the paper is translucent, a sufficient number of test specimens 
shall be stacked one upon another so that no incident light can 
penetrate entirely through them. Two tests shall be made on each 
side of not less than five specimens, one test in the machine direc- 
tion of the paper and one in the cross direction. The test results 
shall be recorded in degrees to the nearest 1/5 degree. The aver- 
age degrees of gloss shall be computed and converted to per cent 
gloss by formula: 

Per cent gloss = cos 2 (60 degrees — degrees gloss) x 100 

Duplicate determinations shall agree within 0.5 per cent gloss. 
IV. Report: 

The results shall be reported in per cent gloss to the nearest one- 
tenth per cent. The average, maximum and minimum gloss shall 
be reported. Where required in order to show the difference in 
finish between the two sides of the paper the gloss of each side 
shall be reported separately. 


V. References: 


“The Glarimeter—An Instrument for Measuring the Gloss of Paper,’ by 
R. L. Ingersoll. Journal Optical Society of America, May, 1921. 

‘“‘An Improved Form of Glarimeter,” by R. L. Ingersoll. Paper 27, No. 23, 
18 (Feb. 9, 1921). 

““A Means to Measure the Glaze of Paper,’’ by R. L. Ingersoll. Electrical 
World 63, 645 (Mar. 21, 1914); Pulp and Paper Magazine of Canada 12, 233 
(Apr. 15, 1924). 

“Determination of Glare,’ by R. L. Ingersoll. Electrical World 64, 35. 

““An Improved Form of Pickering Polarimeter for Gloss Measurements (by 
the Polarization Method).’”? A paper presented before the Fifth Meeting 
(Dec. 27-29, 1920) of the Optical Society of America (at the University of 
Chicago), by R. L. Ingersoll. 


“The Ingersoll Glarimeter.’’ Bulletin No. 100, Central Scientific Company, 
Chicago, Il. 

For a description of the Pickering Polarimeter, see Proceedings American 
Academy Arts and Sciences, 9, 1 (1873); also 21, 294 (1885). 

“The. Glarimeter and the Measurement of the Finish of Paper,’ by R. E. 
Lofton. Paper Trade Journal 80, No. 7, 47-49 (Feb. 12, 1925). 


20. Surface Texture 


A. G. Rendall has described a way of measuring the surface 
texture of paper by means of the “slip” method. One piece of the 
paper under test is fastened on the face of a block of wood and 
another piece on the surface of an inclinable plane. The latter 
is raised until the block starts to slip when the angle of inclination 
is measured. Care must be taken not to touch the test surfaces 
with the fingers. 

21. Volumetric Composition’ 


The determination of the volume composition of a paper is at 
best only an approximation but it is at times desirable to carry it 
out. The weight of a cubic centimeter of the paper is first ascer- 
tained by calculation from the thickness of the sample and the 


8 Chemistry of Pulp and Paper Making, by Edwin Sutermeister, Chapter 
15, pages 386-428, 


CONDUCTING PARTICLES 97 


weight of a measured area. The percentage by weight of the vari- 
ous materials present, fibers, clay, size, etc., is then determined in 
the usual way and from this the weight of each cubic centimeter 
of the paper is calculated. The weight of each substance in grams 
divided by its specific gravity gives the volume occupied by it, and 
the sum of all of these volumes subtracted from 1.0 gives the 
volume of air per cubic centimeter of paper. This method is 
fairly accurate when only fibers, clay and rosin are present but 
when other substances are added as in coated papers, the problem 
becomes more complex and the results less reliable. 

If the volume of air per cubic centimeter of paper is the only 
information needed it may be obtained by determining the actual 
specific gravity by weighing in air and then 1n oil of known density 
exactly as in making specific gravity determinations in water. It 
will be found hecessary to expose the paper, submerged in oil, to 
reduced pressure for some time in order to be sure that all air is 
removed and replaced by oil. 


22. Conducting Particles 


To show the presence of conducting particles in paper 0.5 or 0.75 
mils thick, the sample is placed upon a metal plate which has 
been polished to a smooth plane surface. This plate is connected 
in series with three dry cells, a model 280 Weston voltmeter of 
3-volt range or a similar instrument, and a metal piece which has 
a perfectly flat undersurface and will be in contact with all parts 
of the plate upon which it rests. This metal piece is about 1 inch 
long and ¥% inch wide and is attached to a handle for convenience 
in using. It is called the detector. To test paper, place a measured 
area upon the plate, make contact with the metal detector and the 
plate and if there is deflection of the voltmeter the instrument is 
ready to use. Pass the detector slowly over the paper on the 
plate using light pressure. When a deflection of the voltmeter in- 
dicates that there is a conducting particle in the sheet between the 
detector and the plate, the position of the detector is marked on the 
paper and it is then moved over the spot at right angles to its 
former position and the paper marked when deflection again oc- 
curs. This locates the particles within a half-inch square and 
makes them available for microscopic study. Results are ex- 
pressed in terms of number of conducting particles present per 
square foot of paper. With the thicker papers the particles cannot 
be registered with dependable accuracy because they seldom extend 
through the full thickness of the sheet. Comparison of iron par- 
ticles present as shown by chemical tests gives numbers far in ex- 
cess of the number of iron particles that are actual conductors in 
the sense of spoiling the paper for electrical purposes. This instru- 
ment is intended for use in testing papers specified for use in 
electrical equipment. 


98 PHYSICAL SPiN 


A modification of the apparatus described 1s shown in Fig 3]. 
Here the metal base and the detector are connected in series with 
two dry cells and a radio head set. The presence of a conducting 
particle is indicated by a click in the telephone receivers. 


23. Extractor and Friction Cleanser 


An apparatus has been developed by F. T. Carson for removing 
the film of carbon and binding materials from carbon paper in or- 
der that the tissue base may be tested. It is so constructed that 
vapors from a boiling solvent are condensed and fall on the paper 
on a rotating drum against which a felt friction pad bears. The 
combination of solution by the hot solvent and friction of the felt 
pad removes the carbon film rapidly and completely. The appara- 
tus may be used for various other processed papers such as paraf- 
fined and asphalted papers. It is illustrated by Fig. 32. 


24. Retention of Filler 
By retention of filler is meant the proportion of the total amount 
of filler added to the beater that is retained in the paper. Where it 
is desired to make a mill test of retention the following formula 
suggested by E, Sutermeister is recommended: 


0.94B (100 —C—A) 
Per cént retention = —— eee 
A(100—C=B3 


PyG. 31. 


Apparatus for Detecting Conducting Particles. (Bureau of Standards.) 


RETENTION.OF FILLER __ 99 


Bre 32. 


Extractor and Friction Cleanser. (Bureau of Standards.) 


in which 
A = Per cent of ash in bone dry stock going to the paper machine 
from the beaters. 
B = Per cent of ash in bone dry paper at machine reel. 
C = Per cent of bone dry filler lost on ignition. 


The figure 0.94 is the average amount of material other than 
filler retained on the paper machine. In twenty paper machine runs 
made at the Bureau of Standards, using 20 per cent of filler, the 
average loss agreed exactly with this figure. This figure may vary 
in different mills and it is advisable in each mill to find if it 1s 
applicable to the particular conditions obtaining in that mill. 

Where it is desired to estimate the amount of filler to be used 
from an analysis of paper, the calculation is more involved. The 
following formulas were devised for this purpose. The percent- 
ages are used in the formulas as whole numbers to the first deci- 
Mia piace, te, 11 the per cent of ash in the paper is 10.2,: this 
figure is substituted for A in the formula. 

Secure about a 5 pound sample of the filler to be used, being 
Careiul to select a representative sample.. Break up all lumps, 
spread on a flat surface, divide into four parts, by dividing the pile 
by two lines at right angles to each other crossing at the center 
of the pile. Select two opposite quarters, mix and proceed as 
before. This is known as the “quartering method of sampling.” 
This quartering method is continued until about 25 grams of load- 
ing material are obtained, which are then placed in a bottle for 
further use. From this bottle remove a 1 gram sample, dry at 105 
degrees C. to constant weight and calculate per cent of moisture 
in the loading material. Place the dried residue in a crucible and 
heat at the full heat: of meker burner until a constant weight is 


100 PHYSIGAL “FESTING 


secured, then calculate the per cent of water of composition in the 
dry clay. 
(Have clay in a finely divided state and stir frequently during 
burning). 
Secure sample of pulps to be used and determine per cent of 
moisture and per cent of ash. Weigh the pulp added to the beater. 
-Weigh the clay added to the beater. After running the paper over 
the paper machine, secure several pieces as a representative sample; 
dry and make the ash determination on the paper. The aforemen- 
tioned data used in the following formula will give the per cent of 
clay used and the per cent retention. 


Let P = Weight of pulp added (in pounds). 
C = Weight of clay added (in pounds). 
A = Per cent ash in the finished paper. 

Ap = Per cent ash in the pulp. 
Wc = Per cent water of composition in the ciay. 
Mp = Per cent moisture in the pulp. 
Mc = Per cent moisture in the clay. 
100° X= 
(1) Per cent of clay used = -————— 
P 
106: AS > ase 
(2) Per cent retention = ———__—_ 
C (100—A) 
100 C (1—Mc) 
(3) Per cent of clay used = ———————— 
P (1—Mp) 


100 PX (A—K) 
C (100—A—K) 


(4) Per cent retention = 


The value of K is the per cent of filler not derived from the 
loading added. An average value of K is 0:50 so that the formula 
(4) may be used as foregoing or as follows: 


(5) Per cent retention So, ee ee 
C (100—A—0.5) 


Formulas (3) and (5) are recommended for use by the Tech- 
nical Association of the Pulp and Paper Industry, although (1) 
and (2) may be used when accuracy is not essential or when the 
values for moisture content are unknown. Formula (4) does not 
take into consideration the per cent water of composition in the 
loading. Where this is known suitable correction may be made. 


No account is taken of the ash from alum or rosin size as the 
maximum amount from these factors is probably under 0.05 per 
cent and therefore negligible. An ash determination need not be 
calculated beyond the first decimal place. (See ash determination 
under chemical testing.) 


The following formula has been suggested by José de la Ma- 
corra, Jr., for use where “broke” paper is a part of the beater 
furnish: 

10,000: XO" & 
(100—p) [P(100—Hc) + me Mc + 0.5A] 


Percentage retention = 


Hige 30: 
(Foreign Paper 


Schopper Expansion Tester. Mills, New Vork <Noi¥s) 


10) 


102 PHYSICAL TESTING 


in which 


Per cent of ash in the examined paper. 

Weight of total fibrous material furnished to beater. 
Per cent of bone dry filler lost on ignition. 
Weight of filler furnisher to beater. 

Per cent of moisture in filler. 

Per cent of filler in ‘‘broke’’ used. 

Weight of ‘‘broke’’ paper furnished to beater. 
Weight of pulp furnished to beater. 


me oe WO 
WAP AE TE WU 


25. Expansion and Contraction of Paper 


a. SCHOPPER EXPANSION TESTER 

In this device a strip of paper 1s fastened vertically between twu 
clamps, the lower one fixed and the upper one movable. The strip 
of paper is kept under slight tension by means of a small weight 
attached to a cord which passes over a pulley and is fastened to 
the movable clamp. The specimen, having first been clamped in 
place with the pointer indicating zero, is then immersed in water 
by bringing up a vessel of water. from below until it is submerged. 
The movement of the upper clamp communicates a magnified 
movement to a pointer which indicates on a scale the per cent 
change in length of the strip due to change in the amount of mois- 
ture in the paper. If the vessel of water is removed so as to allow 
the specimen to lose moisture the contraction of the strip of paper 
as it dries is indicated on the scale as the pointer moves in the op- 
posite direction. By replacing the vessel of water by a chamber 
through which conditioned air circulates the apparatus may be 
used to measure expansion or contraction with changes in humidity 
of the air. (Fig. 33). 

b. Davis (PAperR, JANUARY 10, 1923) 
describes an apparatus for measuring expansion and contraction. 
One or more strips of paper are suspended vertically in a water- 
jacketed tube by clamping them rigidly by the upper ends and fas- 
tening the lower ends to counter-balanced pointers which move 
over a graduated scale and are so constructed so as to magnify 
the movement of the paper strips. Air, conditioned by bubbling it 
through sulphuric acid of proper concentration, is passed through 
the tube until the pointers come to rest.. The air stream is then 
switched to other sulphuric acid solutions of different known con- 
centration so as to expose the strips of paper to air of a different 
humidity until the pointers again come to rest. The expansion or 
contraction due to the change in humidity can then be read on 
the calibrated scale. 

R. C. Griffin has described (Paper Trade Journal, 85 No. 5, 
Aug. 4, 1927) an improved form of this apparatus which is shown 
in Fig. 34. 

c. If the expansion and contraction test can be carried out in a 
humidity room in which the humidity can be varied at will, a simple 
procedure is as follows: At two points some 10 inches apart in the 
direction in which the determination is to be made wide marks are 


EXPANSION AND CONTRACTION 103 


Fic. 34. 
Griffin Expansion Tester. (Arthur D. Little, Inc., Cambridge, Mass.) 


made with a glass marking pencil. In each of these marks a fine 
line is made with a razor blade perpendicular to the line joining 
the two points. A scale graduated to hundredths of an inch is 
used to measure a distance between these two fine reference 
lines. By the use of a magnifying glass, the zero line of the scale 
is made to coincide with one of the razor marks. The scale read- 
ing opposite the other razor mark can then be determined to thou- 
sandths of an inch by the use of the magnifying glass and estimat- 
ing the third decimal place. By taking readings in this manner 
after the paper has come to equilibrium at different humidities the 
amount of expansion or contraction is determined. 

d. The expansion of boards is easily determined by means of 
one or more extensometers such as those shown in Fig. 35, this 
particular form being devised by the Bureau of Standards. In 


104 PHYSICAL VCESTING 


each extensometer one end of the board whose expansion is to be 
measured rests against the short lever arm of the pointer and the 
other end of the specimen rests against a stop which 1s adjustable 
so as to bring the pointer to zero on the scale at the beginning of 
the test. As the board expands the pointer moves over the scale 
which is graduated so as to show the expansion directly in per cent 
of the original length of the specimen. Such extensometers may 
be used in a humidity room or in a humidity cabinet. 


26. Color. 


A very thorough discussion of various color systems and means 
of measuring color is contained in an article by Gardner and Parks, 
“A Study of Color Systems, Colorimeters and Spectrophotometers” 
(Circular No. 191, Paint Manufacturers Association of the United 
States, 2201 New York Avenue, Washington, D. C.) In this paper 
an attempt has been made to describe, classify and comment upon 
the various systems of color nomenclature and to indicate the use- 
fulness and limitations of various colorimeters and spectrophoto- 
meters. A large number of references to color literature is in- 
cluded. Some of the commercial color measuring instruments now 
available have been found to give satisfactory service in labora- 
tories. 


References: 

“A Measure of the Color Characteristics of Whi‘e Papers.’—Lofton, Bu- 
reau of Standards Technologic Paper No. 244. Describes an application otf 
the Pfund colorimeter. 


Fig, 35, 


Extensometer for Measuring Expansion of Paper Boards. 
(Bureau of Standards.) 


SLIFPNESS 105 


“A Study of the Eastman Universal Colorimeter for Determining the Color 
of Paper.’—Peckham and Brecht, Technical Association Papers, Series IX, 
No. 1, June, 1926. 

“Color Measurement by the Ives Tint Photometer.’’—Baird, Forest Prod- 
ucts Laboratory. Paper Trade Journal 84, No. 17 (Apr. 28, 1927). 

27. Stiffness 

Various methods have been proposed for determining the degree 
of stiffness of non-creasing papers, that is, heavy papers that 
break when they are creased. Bragg described an apparatus de- 
vised by him (Paper, Nov. 20, 1924) which consists of a wooden 
support with a means for clamping one end of a strip of the paper, 
2 x 15 inches, in a horizontal position, and an arbitrary scale for 
indicating the degree of bending. The free end of the paper acts 
as a scale pointer. A similar apparatus is used by Schulz and 
Ewald (Papier-Fabricant, 23, 768-770, 1925). They use a strip of 
paper.20 x 80 mm. and move a weight of the paper toward the 
free end until the paper bends. The distance of the weight from 
the clamp is taken as the measure of the stiffness. 


IV. CHEMICAL ANALYSIS 


1. Official Method for Quantitative Determination of 
Moisture of Paper 
I. Apparatus: 


The special apparatus required for this determination is an air- 
tight container in which the specimen is dried and weighed. For 
the minimum size specimen designated, a weighing bottle approxi- 
mately 65 mm. (2.56 inches) in height and 45 mm. (1.77 inches) in 
diameter is suitable. For larger specimens, proportionately larger 
containers should be used. 

The oven used to dry the paper shall be equipped with means 
for ensuring adequate temperature control and air circulation and. 
preferably equipped with means of drying the air entering the 
oven. 

II. Specimen: 


The specimen for test shall consist of not less than 2 grams of 
paper obtained by cutting small strips from different portions of 
the test sample in such a way as to be representative of it. 

Note: When the paper under test is not in moisture equilibrium 
with the surrounding atmosphere, care must be taken to minimize 
the time of exposure of the test sample to the atmosphere as 
much as possible, gain or loss of moisture being very rapid under 
this condition. 

III. Method: 


The specimen shall be placed in a weighed air-tight container, the 
container closed and the weight of the specimen obtained. The 
cover of the container shall be removed and the paper dried in the 
container, in an oven having an adequate circulation of air, at 
100 to 105 degrees C. (212 to 221 degrees F.), for one hour. The 
container shall then be closed in the oven, removed to a desic- 
cator and cooled in the desiccator to room temperature. The con- 
tainer and paper shall be weighed and the entire process repeated 
until the weight is constant. All weighings shall be made to an 
accuracy of 1 mg. The percentage results of duplicate determina- 
tions of moisture shall agree within 0.2. 

IV; Report: 

The amount of moisture shall be reported-as a _ percentage, 
(1) of the original weight of the paper and (2) of the bone dry 
paper, to the nearest 0.1. 


2. Official Method for Quantitative Determination of Ash 
in Paper 
I. Apparatus: 
A crucible, such as platinum, alundum or porcelain, which will 
not change in weight under the ignition conditions used and 
with a tightly fitting lid; a balance sensitive to 1 mg.; and a 


106 


MINERAL FILLER 107 


desiccator, are necessary for this determination. An electric 
muffle furnace is recommended for burning the paper. 


II. Specimen: 

The test specimen shall consist of not less than 1 gram of air dry 
paper obtained by cutting small strips from different portions 
of the sample in such a way as to be representative of it. 


IlI. Method: 

The specimen of paper shall be weighed in the crucible and com- 
pletely ignited. To avoid loss of small particles of the specimen 
care must be taken to heat it slowly and to protect the con- 
tents of the crucible at all times from strong drafts. When 
the paper is completely burned, as indicated by absence of black 
particles, the crucible shall be removed to. desiccator, covered 
and allowed to remain until its temperature has reached equilib- 
rium with that of the surrounding atmosphere. The crucible and 
contents shall then be weighed and the ignition and weighing 
repeated until the weight is constant. All weighings shall be 
made to an accuracy of 1 mg. The percentage results of dupli- 
cate determinations of ash shall agree within 0.2. 


IV. Report: 
‘The amount of ash shall be reported as a percentage of the air 
dry paper to the nearest 0.1 per cent. 


3. Official Method for Analysis of Mineral Filler in Paper 
I. Specimen: . 

The specimen for test shall consist of not less than 0.2 grams 
of ash obtained from the paper by the official method for deter- 
mining the ash of paper. 

IT. Method for Qualitative Determination: 

Warm the ash in a small quantity of dilute hydrochloric acid. 
An effervescence indicates the presence of carbonate. If there 
is an insoluble residue, decant the acid solution through a filter 
paper and repeat the operation twice, finally transferring the 
residue to the filter paper and washing it thoroughly. 

Add an excess of ammonium hydroxide to a portion of the 
acid solution. A white, gelatinous precipitate shows the pres- 
ence of aluminum. Filter off any such precipitate and add a 
solution of ammonium oxalate. A white granular precipitate 
indicates calcium. To another portion of the acid solution add a 
few drops of barium chloride and warm. A white precipitate 
will form if a sulphate compound is present. 

Dry any residue from the acid treatment of the ash, burn off 
the filter paper in a platinum crucible, and add to the contents 
of the crucible, a fusion mixture consisting of equal parts of 
sodium and potassium carbonates. Fuse to a clear mass, cool, 
transfer the fusion to a beaker and heat gently with water. When 
the mass is thoroughly disintegrated, filter and wash any residue 


108 CHEMICAL ANALYSIS 


thoroughly with hot water. To the filtrate add an excess of 
hydrochloric acid, evaporate to dryness, and treat the residue 
with a warm solution of dilute hydrochloric acid. A white, trans- 
parent, flaky precipitate shows the presence of silica. Filter off 
such precipitate and add a solution of barium chloride when a white 
precipitate will form if an insoluble sulphate, such as barium sul- 
phate, was present in the paper. Dissolve the water-insoluble 
portion of the fusion with dilute hydrochloric acid. Add to the 
solution an excess of ammonium hydroxide and boil. A white 
gelatinous precipitate. shows the presence of aluminum, Filter 
off any such precipitate and add ammonium carbonate to the fils 
trate, a white precipitate occurring if barium is present. Filter 
and. add an excess of ammonium phosphate and stir thoroughly 
after cooling. A white crystalline precipitate indicates magnesium. 

A considerable amount of calcium and sulphate in the ash sol- 
uble in hydrochloric acid indicates the presence of calcium 
sulphate, CaSO.2H,O (crown filler). The presence of barium 
and sulphate in the acid-insoluble portion of the ash indicates 
barium sulphate, BaSO,; (blanc fixe, or barytes). An alkaline 
ash containing calcium soluble in hydrochloric acid but with no 
sulphate present indicates the presence of calcium carbonate 
CaCO; (whiting or chalk). The presence of barium in ash which 
is soluble in hydrochloric acid with effervescence indicates bar- 
ium carbonate, BaCQO;. Ccnsiderable amounts of silica and alum- 
inum indicate aluminum silicate added as china clay. Consider- 
able amounts of silicate and magnesium indicate magnesium sili- 
cate. derived from tale or asbestine. A microscopical examina- 
tion of the ash assists in determining the variety of silicious 
minerals present. 


III, Method for Quantitative Determination: 


The procedure for determining the amounts of the various 
fillers present follows that given for the qualitative determina- 
tion of them. The methods used for ensuring quantitative sep- 
aration and determination of the various constituents are those 
described in standard textbooks dealing with mineral analysis. 
When the ashing of the paper causes chemical changes in the 
filler, the actual amount of filler originally present must be cal- 
culated. The more common examples of such changes are: loss 
of combined water in clay and crown filler; loss of carbon diox- 
ide ‘in carbonates; reduction of sulphates to sulphides. 


IV. References: 
Technical Methods of Analysis, by R. C. Griffin. 


4. Official Method for Analysis of Mineral Coating of Paper 
if Specimen: 

The specimen for test shall consist of the equivalent of not 
Jess than 0.2 grams of mineral coating obtained by separation 


AMOUNT OF COATING 109 


from the basic paper as described in the official method for deter- 
mination of amount of coating. 
If. Method: 

The method of analysis is the same as described in the official 
method for analysis of mineral filler. If the coating yields an 
acid-solution portion containing calcium, aluminum, and sulphate, 
the presence of satin white is indicated. If calcium is found 
but no sulphate, and if the coating gives an effervescence with 
hydrochloric acid, it contains chalk or whiting (CaCOs). If the 
coating contains carbonates, is free from calcium and magne- 
sium, and contains acid-soluble barium, the presence of barium 
carbonate (BaCO;) is indicated. The presence of barium and 
sulphate in the portion insoluble in hydrochloric acid indicates 
blanc fixe or barytes (barium sulphate, BaSO.). The presence 
of silicate in the acid-insoluble portion (1), with aluminum indi- 
cates clay, and (2) with magnesium indicates talc or asbestine. 
Ill. Reference: 

Technical Methods of Analysis, R. C. Griffin. 

5. Official Method for Determination of Amount of Coating 
of Mineral Coated Paper 
I. Apparatus : 
No special apparatus is required for this determination. 
IT. Specimen: 

The specimen for test shall consist of a piece of the sample cut 
box bo eo. (2 x 5 inches). 
Ill. Method: 

Obtain the air dry weight of the specimen. Place the speci- 
men in a flat bottom tray and pour over it a warm 5 per cent ~ 
solution of hydrochloric acid. After a few moments pour off the 
excess acid and add a warm 5 per cent solution of ammonia, 
moving the paper around so that the solution comes in contact 
with all parts of it. After this treatment has continued for a 
few minutes, place the paper on a pane of glass and brush off 
the coating with a camel’s-hair brush, taking care not to dislodge 
any of the paper fiber. After the coating is entirely removed, 
stand the glass pane at a slight angle and wash the paper by 
means of a wash bottle, holding the paper on the glass by one 
corner. Dry the specimen and obtain the air dry weight. The 
difference between this weight and the original weight of the 
specimen is the amount of coating material present. Not less 
than two determinations shall be made, and the average of these 
computed. 

IV. Report: 

The amount of mineral coating shall be reported, (1) as a per- 
centage of the decoated air dry paper and, (2) as pounds per 
500 sheets of the decoated air dry paper 25 x 40 inches in size. 
The weight of the decoated air dry paper on this same weight 
basis, shall also be included in the report. 


110 CHEMICAL:ANALYSIS 


V. Reference: 

Suggested by Edwin Sutermeister. 

6. Official Method for Qualitative Determination of Casein 
in Paper 

A positive result obtained by the following method shall be 
regarded as. conclusive evidence of the presence of casein in 
paper. 

I, Millon Method: 

Boil 0.5 gram of paper several minutes with 10 cc. of a-1 per cent 
solution of caustic soda. (Caustic soda is required to dissolve 
casein that has been hardened by formaldehyde or other agents.) 
Filter off the aqueous extract, cool to room temperature, add a 
suitable indicator such as phenolphthalein and exactly neutralize 
with nitric acid. Add several cc. of Millon’s reagent prepared as 
follows: Dissolve 20 grams of chemically pure mercury in 40 
grams of concentrated chemically pure nitric acid and dilute the 
solution to 180 cc. with distilled water. Upon heating the presence 
of casein is indicated by the development of a red coloration. 
(This reaction is dependent on the presence of tyrosine which 
occurs in casein to the extent of approximately 5 per cent, but has 
been reported only in rare instances as occurring in animal glue 
and gelatine, and then only in doubtful traces.) 


7. Official Method for Qualitative Determination of Rosin 
in Paper 

A positive result obtained by both of the following methods 
shall be regarded as conclusive evidence of the presence of rosin 
in paper. 

I. Lieberman-Storch Method: 

Place 1 gram of paper cut in small pieces in a clean, dry test 
tube. Add 5 cc. chemically pure acetic anhydride and boil down to 
about 1 cc. (The fumes of anhydride are very irritating and 
should be burned as they leave the test tube.) Pour the liquid 
residue into a clean, dry porcelain crucible and cool to room temper- 
ature. If any waxy particles separate, they should be filtered off. 
Add carefully, down the side of the crucible, one drop of con- 
centrated sulphuric acid. A fugitive rose-violet coloration formed 
when the acid meets the anhydride indicates rosin. 

II. Raspail Method: 

Place the paper on a glass or porcelain plate and apply a drop 
of strong solution of sugar. After a few moments remove excess 
sugar solution with filter paper. Add a drop of concentrated sul- 
phuric acid to the sugar on the paper. A raspberry-red coloration 
indicates the presence of rosin. 

8. Official Method for Quantitative Determination of Resin 
in Paper 
I, Apparatus: 
A suitable extraction apparatus such as the Soxhlet or the Un- 


RESIN 111 


derwriter’s is especially required for this determination. In addi- 
tion, if glue or other nitrogenous sizing agents are present, two 
300 ce. separatory funnels are necessary. The balance used shall 
be sensitive to 1 mg. 

Il. Specimen: 

The test specimen shall consist of not less than 5 grams of 
paper obtained by cutting strips approximately % inch wide from 
the sample in such a way as to be representative of it. It is 
recommended that the specimens be shredded or ground. 

Ill, Method: 

Obtain the air dry weight of the specimen. If the paper is not 
shredded or ground, fold the strips into numerous crosswise 
folds and place them in the siphon cup of the extractor. Ex- 
tract with acidulated alcohol, (95 per cent alcohol—90 per cent, 
glacial acetic acid—0.5 per cent, water 9.5 per cent by volume) 
siphoning at least 12 times or as many more as may be neces- 
sary until the solvent siphons over colorless. If nitrcgenous siz- 
ing agents are present, they must be separated from the resin 
as follows, this not being necessary in absence of such materials. 
Wash the alcoholic extract of resin, which may contain foreign 
material, into a beaker and evaporate to a few cubic centimeters on 
a steam bath. Cool, take up in about 25 cc. of ether, transfor to a 300 
ce. separatory funnel containing about 150 cc. of distilled water 
to which has been added a small quantity of sodium chloride to 
prevent emulsification, shake thoroughly and allow to separate. 
Draw off the water into a second separatory funnel and repeat 
the treatment with a fresh 25 cc. portion of ether. Combine the 
ether extracts which contain the resin and any other ether-soluble 
material, and wash twice or until the ether layer is perfectly 
clear and the line between the ether and the water is sharp and 
distinct, with 100 cc. portions of distilled water to remove salts 
and foreign matter. Should any glue, which may be extracted 
from the paper, interfere by emulsifying with the ether, it may 
be readily removed by adding a strong solution of sodium chlor- 
ide to the combined ether extracts. Shake thoroughly and draw 
off the aqueous solution repeating if necessary before washing 
with distilled water. Transfer the alcoholic or the ether extract 
to a weighed evaporating dish, evaporate to dryness, dry the resi- 
due exactly 1 hour at 100 degrees C., and weigh to an accuracy 
of 0.1 milligram. Not less than two determinations shall be made, 
and the average of the results computed. The percentage results 
of duplicate determinations of resin should agree within 0.2. 

IPs. Keport: 

The resin content shall be expressed as a percentage of the 

air dry paper, to the nearest 0.1 per cent. 


V. References: 


“Quantitative Determination of Rosin in Paper.”—C. F. Sammet, Ind. & 
Hung. Chem, 5, 732 (Sept., 1913); Paper 13, No. 1, 17 (Sept. 17, 1913). 


riZ CHEMICAL ANALYSIS 


9. Official Method for Qualitative Determination of Nitro- 
genous Proteinaceous Materials in Paper 


A positive result obtained by the following method shall be 
regarded as conclusive evidence of the presence of nitrogenous 
(proteinaceous) materials, such as glue and casein, in paper. 
T, » Ammonium Molybdate Method: 

Boil 0.5 gram of paper for several minutes with 10 cc. of a 1 per 
cent solution of caustic soda. (Caustic soda is necessary as tke 
nitrogenous materials may have been made insoluble in water by 
hardening treatment with formaldehyde or other agents). Filter 
off the aqueous extract and after cooling add a suitable indicator, 
such as phenolphthalein, then exactly neutralize with hydrochloric 
acid. Prepare Schmidt’s reagent by dissolving 3 grams of chem- 
ically pure ammonium molybdate in 250 cc. of distilled water and 
adding 25 cc. of chemically pure nitric acid of 1.2 specific gravity. 
(This reagent is not permanent and should be made fresh at 
frequent intervals.) Add 1 volume of the reagent to 2 volumes of 
the aqueous extract. A white precipitate shows the presence of 
nitrogenous materials derived from proteins. 

Note. This test is very delicate. If no precipitate or only a 
slight precipitate is obtained there can be no appreciable amount of 
proteinaceous materials present. 


II References: 

Carson, F. T., ‘‘Detection of Animal Size in Surface Sized Papers, 
Trade Journal, April 10, 1924. 

Griffin, R. C., Technical Methods of Analysis. 

Chem. Zeitung, 36, 313 (1912). 

Farber-Zeitung, 24, 97 (1913); Schmidt. 

10. Official Method for Quantitative Determination of 
Proteinaceous Nitrogen in Paper 
I, Apparatus : 

A Kjeldahl digestion and distillation apparatus is required for 
this determination. A 500 cc. Kjeldahl flask is a suitable size. 
The balance used shall be sensitive to 1 mg. 

II Specimen: 

The specimen shall consist of from 3 to 5 grams of air dry paper 
abtained by cutting small strips from different portions of the 
test sample, in such a way as to be representative of it. The 
strips shall be cut into pieces approximately 6 mm. (0.25 inch) 
square. 

III, Meihod: 

The Gunning methcd is used. Place the specimen, weighed to 
an accuracy of 1 mg. in the Kjeldahl flask and add 10 g. of 
powdered anhydrous sodium sulphate, a small crystal of copper sul- 
phate (about 0.2 grams) and 25 cc. of concentrated sulphuric acid. 
Heat the flask gently until frothing has ceased and then digest 
with increasing temperature until oxidation is complete, i.e., for 
a short time after the mixture becomes clear and colorless or 


” 


Paper 


STARCH 113 


nearly so. Cool and dilute with about 200 cc. of distilled water. 
Add about 2 cc. of liquid petrolatum to prevent foaming and 
about 2 grams of 30 mesh granulated zinc to prevent bumping dur- 
ing the distillation. Adda saturated solution of sodium hydroxide 
to the contents of the flask in such amount (usually 75 cc.) that 
there is an excess of 5 cc. of the saturated sodium hydroxide 
solution present. This solution must be poured carefully down 
the side of the flask so that it does not mix with the acid con- 
tents. 

The total volume of the solution should be about 400 cc. Im- 
mediately connect the flask to a condenser having its delivery tube 
just beneath the surface of a known amount of N/10 sulphuric 
acid diluted to 100 cc. (30 cc. of N/10 acid is usually sufficient.) 
Mix the contents of the Kjeldahl flask by shaking the flask, then 
heat it gradually and distill the contents for about 45 minutes, 
taking care to avoid spurting. 

The total volume of the distillate should be about 200 cc. Ti- 
trate the contents of the receiver flask with N/10 alkali, using 
methyl red indicator. The difference between the number of cubic 
centimeters of N/10 alkali used and the cubic centimeters of N/10 
sulphuric acid added to the receiver flask is the number of cubic 
centimeters of N/10 acid equivalent to the nitrogen present. This 
number multiplied by 0.014 is the nitrogen found. The per- 
centage results of duplicate determinations of nitrogen shall 
agree within 0.02. A blank determination shall be made on all 
reagents used and any nitrogen found subtracted. 

IV. Report: 

The amount of nitrogen shall be expressed as a _ percentage 
of the air dry paper to the nearest 0.01 per cent. If it is de- 
sired to report the per cent of glue or a casein present, it shall 
be calculated by multiplying the per cent of nitrogen found by 
5.6 and 6.3 respectively. (Note—As these factors vary with: dif- 
ferent kinds and grades of material they should be determined 
whenever the nitrogenous material is available, and whenever 
possible the nitrogen in the paper before addition of the nitro- 
genous material should be determined and subtracted from the 
total nitrogen found.) | 


11, Official Method for Qualitative Determination of ‘Starch 
in Paper 


A positive result obtained by the following method shall be 
regarded as conclusive evidence of the presence of starch in paper. 

Boil 0.5 gram of paper for several minutes with 10 cc. of water. 
Filter off the extract and cool it. Add one drop of a 0.01 normal 
solution of iodine. A blue coloration indicates starch. If only 
a faint violet coloration is obtained, this should be disregarded, 
as non-starch constituents of paper sometimes give such reaction. 


114 CHEMICAL ANALYSIS 


12. Official Method for Quantitative Determination of Starch 
in Paper 
I, Apparaius . 

A reflux condenser is necessary for this test. The balance used 
for weighing shall be sensitive to 1 mg. 
II. Specimen: 

The specimen shall consist of not less than 5 grams of bone dry 
paper obtained by cutting small strips from different portions of 
the test sample in such a way as to be representative of it. The 
strips shall be cut into small pieces about 6 mm, (0.25 inch) square. 
III. Reagents: 

Fehling’s solution. (a) 69.3 grams of crystalized copper sulphate 
are dissolved in water and the solution diluted to 1,000 cc. (b) 
346 grams of Rochelle salt and 120 grams of sodium hydroxide are 
dissolved in water and the solution diluted to 1,000 cc. Allow to 
stand two days and filter. Solutions (a) and (b) are kept sepa- 
rate and equal volumes of them mixed just before use. 

Indicator solutions. A 10 per cent solution of potassium fer- 
rocyanide, and a 50 per cent solution of acetic acid are used. 

IV. Method: 

Place the weighed specimen of paper in a 500 cc. flask; add 
200 cc. of water and 5 cc. of glacial acetic acid. Connect the 
flask to a reflux condenser and boil the contents vigorously for 
lY% hours. Pour the contents of the flask on the perforated plate 
of a Buchner funnel and wash the pulp on the plate with 50 cc. 
of hot water using suction. Add 15 cc. of 37 per cent hydro- 
chloric acid to filtrate and boil it for 30 minutes, allowing the 
volume to decrease by evaporating to about 200 cc. Neutralize 
the hot solution by adding solid sodium carbonate until efferves- 
cence ceases. Cool to room temperature and adjust to a mea- 
sured volume by means of a volumetric flask. Titrate this solution 
into a measured quantity of Fehling’s solution diluted to 25 cc. 
After each addition of the titrating solution, boil the reaction 
mixture for 1 minute. The end-point is determined on a spot 
plate by adding a drop of the mixture to a mixture of one drop 
each of the ferrocyanide and acetic acid solutions, and is that 
point at which no immediate color is produced on the plate. The 
number of cubic centimeters of Fehling’s solution used multiplied 
by 0.005 is the grams of starch equivalent to the volume of the 
titrating sugar solution used. The results of duplicate determina- 
tions of starch shall agree within 0.05 per cent of the total percent- 
age found. As the factor for converting cubic centimeters of 
Fehlings solution to grams of starch varies with different kinds and 
grades of starch, when the starch used in the paper is available, its 
exact factor should be determined by the following procedure: 

Dry the starch at 100 to 105 degrees C. (212 to 221 degrees F.) 
for 3 hours. Weigh 0.05 gram and boil with about 190 cc. of a 4 


ACAINV EULER 115 


per cent hydrochloric acid solution for 30 minutes. Neutralize 
with solid sodium carbonate, cool, adjust to a definite volume 
and titrate a definite volume of Fehling’s solution as described 
above. 

When it is desired to express the content of starch on an air 
dry basis and the actual initial moisture content of the starch is 
not known, the average moisture figure of 12 per cent may be used 
ian the conversion calculation. 

V Report: 

The amount of starch shall be reported as a percentage of the 
air dry paper to the nearest 0.01 per cent. 
VI. References 


“Quantitative Estimation of Starch in Paper.’—V. Voorhees and O. Kamm, 
Paper 24, folio page 1091 (Aug. 27, 1919). 


13. Official Method for Qualitative Determination of Active 
Sulphur in Paper 
I, Apparatus: 

The special apparatus required for this determination consists 
of a 500 cc. round-bottom distillation flask having a, neck about 
5 cm. (2 inches) long and 25 cm. (1 inch) in diameter, and a tube 
10 cm. (4 inches) long so connected to the mouth of the flask that 
all gases generated in the flask will pass through a filter paper, 
clamped between the mouth of the flask and the end of the tube, 
and then out through the tube. 

The balance used for weighing shall be sensitive to 1 mg. 

IT. Specimen: 

The specimen shall consist of 0.25 gram of air dry paper either 
ground or thoroughly disintegrated by shaking in water. 

III. Reagents: 

Small pieces of chemically pure stick zinc, free from sulphur 
and arsenic, activated as follows. Cover the zinc with chemically 
pure copper sulphate solution in the proportion of 10 cc. of copper 
sulphate solution, containing 0.002 gram copper, to 1 gram of 
zinc. After allowing to stand a few minutes for deposition of 
the copper, wash the zinc with distilled water until free from 
zinc sulphate. The zinc can be reactivated several times. 

Concentrated chemically pure hydrochloric or phosphoric acid, 
free from sulphur and arsenic. 

C. P. lead acetate, 10 per cent solution. 

C. P. sodium thiosulphate, 0.001 per cent solution. 

Sulphur-free surgical absorbent cotton prepared by boiling in 
a dilute solution of sodium hydroxide and washing thoroughly 
with distilled water. 

IV. Method: . 

Transfer the weighed specimen to the distillation flask with 
20 cc. of distilled water and add approximately 2 grams activated 
zinc cut in small pieces, and 10 cc. of concentrated hydrochloric 
or phosphoric acid. Insert in the neck of the flask a loose wad of 


116 CHEMICAL ANALY=lIsS 


surgical absorbent cotton about 4 cm. (1% inches) long. Clamp be- 
tween the mouth of the flask and the tube a hardened filter paper 
(such as Schleicher and Schiills’ No. 575) which has been freshly 
moistened with 10 per cent solution of lead acetate. Place an- 
other wad of absorbent cotton in the tube above the filter paper. 
Prepare flasks under duplicate conditions containing in place of 
the paper under test, pure, sulphur-free cotton, and measured 
amounts of sodium thiosulphate solution. Set all the flasks in a 
steam bath for 1 hour, frequently agitating the contents. KRe- 
move the filter papers and allow them to air dry. The per cent of 
sulphur present is found by comparing the depth of the color devel- 
oped by the sulphur from the specimen with that developed by 
the known amounts of sulphur evolved from the thiosulphate solu- 
tions, 

As 0.000001 gram sulphur will give a distinct stain, care must be 
taken to protect the paper under test from contamination. It must 
be protected from atmospheric fumes and should not be handled 
with the bare hands. 

V. Report: 

The amount of sulphur shall be reported as a percentage of the 
air dry paper. 

Note: In respect to the tarnishing effect of sulphur, a paper 
containing not more than 0.0008 per cent of sulphur is required 
for wrapping silverware. 

VI. Reference: 
Chemistry of Pulp and Paper Making, Edwin Sutermeister, page 422. 


14. Official Method for Quantitative Determination of 


Paraffin in Paraffined Paper 
I. Apparatus: 


A suitable extraction apparatus such as the Soxhlet or the 
Underwriter’s is required for this determination. 

Il, Specimen: 

The test specimen shall consist of not less than 1 gram of paper 
obtained by cutting strips approximately ™% inch wide from the 
sample in such a way as to be representative of it. 

III, Method: 


_ Weigh the air dry paper to an accuracy of 1 centigram. Fold 
the strips into numerous crosswise folds, and place them in the 
siphon cup of the extractor. Extract with carbon tetrachloride 
(CCli) at least 5 times, and more if found necessary. Remove 
the paper and determine its air dry weight. The difference be- 
tween the original weight of the paper and its weight after ex- 
traction shall be regarded as the amount of paraffin present. 
IV. Report: 


The paraffin content shall be expressed as a percentage of the 
air dry paper to. the nearest 1 per cent. 


SPECIAL MATERIALS 117 


15. Coloring Matter? 


Smalt, existing as it does in high class papers, usually without 
admixture with loading materials, can be estimated with sufficient 
accuracy by incinerating the paper, weighing the ash, and making 
a correction for the small proportion of the latter due to the 
fiber, etc. This proportion dces not usually exceed 2 per cent. 
| The ultramarines are of variable and even doubtful composition 
and are best estimated, therefore, by comparing the depth of color 
of the ash with that of standard mixtures of the pigment with 
known proportions of china clay. 

Chrome yellow, orange, etc., also of variable composition, may 
be determined, if necessary, by estimating the lead and chromium 
separately, and calculating the results to the nearest indicated com- 
position. It is scarcely necessary here to describe the full gravi- 
metric process as it is likely to be but rarely required. It will 
be sufficient to say that the lead is precipitated and estimated as 
the sulphate, and the chromium as chromic oxide. 

Prussian blue may be determined approximately by estimating 
the iron by igniting the paper, fusing the ash with sodium car- 
bonate, treating the fused product with hot water, filtering, and 
boiling the residue with dilute hydrochloric acid and a drop or 
two of nitric acid. ‘The solution is then again filtered, and the 
iron and alumina precipitated with ammonia in the presence of a 
little ammonium chloride. The precipitate of iron and aluminum 
hydrates is washed, filtered off, and digested with excess. of 
caustic soda, then filtered again and carefully washed. The resi- 
due, which consists entirely of iron, is washed, dried, ignited, 
and weighed as the oxide. This process also serves for the esti- 
mation of all other iron pigments except the natural pigments, 
ochres, etc. 


16. Tests for Special Materials 


Oils and fats can be estimated by extracting with ether, evap- 
crating the solvent, and weighing the residue. 

Paraffin-wax—Similar to the foregoing, using benzene or petro- 
leum spirit. 

Salicylic acid—This substance is used as a preservative in papers 
required for wrapping foodstuffs. It is extractable with petroleum 
ether, and may be estimated in the solution by diluting the latter 
with an equal volume of 95 per cent alcohol and titrating with 
N/10 alkali, using phenolphthalein as indicator. Each cubic centi- 
meter of N/10 caustic soda is equivalent to 0.0138 grams of sali- 
cylic acid. ; 

Carbolic acid—The estimation of carbolic acid in carbolized 
‘ wrapping paper is frequently required. Commercial carbolic acid 


® “Chemical Analysis of Paper,’’ by H. A. Bromley. Paper 15, No. 6, 17 
(Oct. 21, 1914). 


118 CHEMICAL ANALYSIS 


consists chiefly of cresvlic acid with higher phenols, but little 
real phenol being usually present. Since, however, cresol is prob- 
ably as efficient an antiseptic and insecticide for ordinary pur- 
poses as phenol, the absence of the latter body is of little import- 
ance. Carholic acid may contain tar oils which are, however, quite 
inert. Naphthalene is also likely to be present. 

For the estimation of commercial carbolic acid the bromine- 
absorption method in use for the determination of phenol is 
valueless. The following method, which is based on a process 
originally described by Muter, is suggested: 

From 10 to 20 grams of paper (according to the probable pro- 
portion of acid present) are cut into pieces and extracted with 
a sufficient quantity of alcohol (95 per cent) in a Soxhlet. The 
extract is transferred to a basin, mixed with about half its volume 
of a 10 per cent solution of caustic soda, and the mixed liquids 
evaporated in the water bath to small bulk. Tar oils and naphtha- 
lene, if present, here separate out and may be removed by filtration. 
The liquid is now transferred to a separating funnel and hydro- 
chloric acid added cautiously and with gentle shaking until the 
liquid shows an acid reaction. Means should be taken to prevent 
the mixture from becoming too hot during the process. A little 
brine is now added. The liberated tar acids rise to the surface of 
the liquid which becomes milky from the precipitation ef rosin. 
The whole is now set on one side for a short time to complete 
the separation of the layer of tar acids, after which the resinous 
liquid is drawn off as completely as possible. The residue of oil 
is shaken up with ether or petroleum spirit, transferred to the 
weighed flask, the solvent evaporated off, and the residue weighed. 

Paraffn—The following qualitative test for paraffin known as 
the Dunlop method may be of value for determining the presence 
of paraffin in the presence of rosin. It consists of boiling the 
sample with acetic anhydride and observing the behavior of the 
solution on cooling. If paraffin is present the anhydride becomes 
turbid and the paraffin separates out on the top in a white precipi- 
tate. Less than 1 per cent of paraffin is said to be detected in 
this manner. (Allen’s Commercial Organic Analysts.) 


Formaldehyde—Owing to the increasing use of formaldehyde as 
a preservative and as a hardening agent in paper sizing processes, 
means of detecting this material have assumed considerable im- 
portance. The following method is suggested by Dr. T. C. Bent- 
zen: Cut the specimen of paper into small pieces and immerse 
them for one hour in a 27 per cent solution of sodium hydroxide. 
Add a small amount of resorcinal and heat to boiling. If for- 
maldehyde is present the solution develops a red coloration. Addi- 
tional information will be found in the article “Detection of 
Formaldehyde in Paper,’ Bentzen, Paper Industry 9, No. 4, July 
1927, 


FREE ACID IN PAPER 119 


17. Free Acid In Paper 


Weigh 10 grams of the paper to be tested, tear into small pieces, 
place in a 250 cc. porcelain casserole, and cover with a small amount 
of distilled water. Heat gently for an hour over water bath or 
electric hot plate. Pour off water and wash with small quantities 
of distilled water, adding it to water extract. 

Another casserole is filled with an equal amount of distilled water, 
to which is added two drops of a methyl orange solution (0.1 per 
cent solution in water). To the former is then added N/10 stand- 
ard solution of caustic soda until the color matches the sample. 
The acidity is then expressed in terms of sulphuric acid (H:SO,.). 

An alternate method is as follows: Take a piece of the paper 
six inches square, place in a saucer, and pour over it distilled 
water, and work about with a glass rod for 5 or 6 minutes. Now 
take a blue litmus paper or a little tincture of litmus and test the 
extract when, if either turns red, it shows the presence of acid. 
Divide the extract into two parts; to one add a few drops of 
nitric acid, then nitrate of silver solution when, if a white, curdy 
precipitate is formed, it proves the presence of hydrochloric acid 
or chlorides. To the second portion add a few drops of hydro- 
chloric acid, heat to boiling in a test tube, and add a solution of 
barium chloride; a white precipitate indicates the presence. of 
sulphuric acid or sulphates. 


V. BIBLIOGRAPHY 


A partial list of reference books and articles in periodicals— 


31. 


32. 


1. Books 


The Chemistry of Paper Making, by R. B. Griffin and A. D. Little. 
Chap. 9, pp. 400-451. 


Allen’s Commercial Organic Chemistry. Vol. 1, pp. 465-480. 


Chemistry of Pulp & Paper Making, by Edwin Sutermeister. Chap. 
15, pp. 386-428. 


Elementary Manual of Paper Technology, by R. W. Sindall. Chaps. 9, 
10, 11,12) pp.: 107-213: 


Engineering Chemistry, by T. B. Stillman. Fifth edition, pp. 561-568. 


Handbuch der Papierkunde (Hand-book of paper technology), by Paul 
Klemm, pp. 248-327. 


Modern Pulp and Paper Making, by G. S. Witham, Sr. Chap. 17, 
pp. 462-500. 


Paper and Its Constituents, by H. A. Bromley. Part III, pp. 141-212. 
Paper, Its History, Source and Manufacture, by H. A. Maddox. 

Paper Prtiifung (Paper Testing(, by Wilhelm Herzberg. 

Technical Methods of Analysis, by R. C. Griffin, pp. 337-363. 


A Text Book of Paper-Making, by C. F. Cross and E. J. Bevan. Chap. 
14, pp. 371-402, 


2. Articles 


Absorbency of Paper, by E. O. Reed. Paper, Vol.-21, No. 19, p. 14, 
Jan. 16, 1918; Jour. Ind. & Engr. Chem., Vol. 10, p. 44, Jan. 


1918. 
Absorption Power of Paper Testing. Paper, Vol. 29, No. 22, p. 12, 
Feb. 1, 1922. 


Alum in Paper, Test for. World’s Paper Trade Review, Vol. 75, p. 12. 

Animal Size in Paper. Paper Makers’ Monthly Jour., Nov. 15, 1919: 
Paper, Vol. 25, p. 622 (1919). ' 

Asbestos Paper, Estimation of. Paper, Vol. 23, folio p. 117, Oct. 9, 
1918. 

Ash Content of Paper, by Hans Wrede. Paper, Vol. 6, No. 7, p. 13, 
Jans 31521912: 

Ash Tests and Their Significance, by F. E. Plumstead, Pulp and Paper 
Magazine of Canada, Vol. 14, No. 2, p. 31, Jan. 15, 1916, Paper, 
Vol. 17, No. -20, p.16, Jan-126, 1916. 

Bag Paper Testing, Lime and Cement, by P. L. Houston, Tech. Papers 
No. 187, Bureau of Standards; Pulp & Paper Magazine of Canada, 
Vol. 18, p. 947, Sept. 9, 1920; Paper, Vol. 27, p. 15, Sept. 22, 1920. 

Balance Pocket Quadrant Demy. Paper Makers’ Monthly Journal, Vol. 


So poe 

Blue and Brown Print Paper, by F. P. Veitch, C. F. Sammet and E. O. 
Reed, Jour. Ind. & Engr. Chem., Vol. 10, p. 222, Mar., 1918. 

Blotting Paper, The Testing of, by P. L. Houston and R. H. Ledig. 
PapER TraDE JourNAL, Vol. 73, No. 19, p. 88, No. 10, 1921. 

Blotting Paper, Technology of. Paper, Vol. 20. No. 10. p. 16, 
May 16, 1917. 

Bulker, Measuring by Perkins Pressure. Paper, Vol. 19, No. 4, p. 86, 
Oct. 4, 1916. 

Bursting Strength of Paper, Conditions Which Influence the, by D. C. 
Douty. Paper TrapE Journat, Vol. 50, No. 6, 271, Feb. 10, 1910. 

Cardboard, The Testing of—for elasticity, rigidity and folding, by R. 
Isnard. Chem. Abstr., Vol. 15, p. 3205, Sept. 20,-1921; Paper 
TRADE JouRNAL, Oct. 20, 1921. 


. Chemical Analysis of Paper, by H. A. Bromley. Paper, Vol. 15, No. 


6, p. 17, Oct, 21; 1914; 

Cigarette Papers, Chemical Analysis of, by Strand Jordan. Jour. of 
Ind. & Engr. Chem., Vol. 8, No. 9, p. 812, Sept., 1916; Paper, Vol. 
19° Noo 16, p13.) Nove 15, 1916; 

Coated Papers & Their Constituents, The Manufacture & Technical 
Examination of, by H. A. Bromley. Pulp and Paper Mag. of Can. 
Vol. 13)" No. 1752p. +463, 5ept. 1, 1915, 

Color, The Measurement of, by C. E. K. Mees, Jour. Ind. & Engr. 
Chem., Vol. 13, No. 8, p. 729, Aug., 1921. 

Color Measurements. PAPER TRADE JouRNAL, July 8, 1920, p. 58. 


120 


BIBLIOGRAPHY 121 


Color, A Means of Accurately Matching (Ives Tint-Photometer), by 
Otto Kress and G. C. McNaughton. Paper, Vol. 18, No. 21, p. 13, 
Aug, 2, 1916. 

Color System, An Examination of the Munsell, by I. G. Priest. Tech- 
nologic Papers, No. 167, Bureau of Standards. } 

Dirt in Paper, Identifying, by D. M. McNeale. Paper, Vol. 24, folio 
p. 1058, Aug. 20, 1919. 

Expansion of Paper, Relation of Moisture and Paper, by E. Suter- 
meister. Paper TRADE JouRNAL, Vol. 59, No. 27, p. 44, Dec. 31, 
1914. 

Fiber Analysis, Microscopic Paper, by G. K. Spence and J. M. Krauss. 
Paper, Vol. 20, No. 11) p. 11..May. 23, 1917. 

Fiber Analysis, Paper. Paper, Vol. 17, No. 3, p. 19, Sept. 29, 1915. 

Fiber Board, Effect of Varying Humidities, by Otto Kress and G. C. 
McNaughton. Paper, Vol. 22, folio p. 251, May. 22, 1918. 

Fiber Board, Impact Test for, by E. O. Reed and F. P. Veitch. Paper, 
Vol. 24, folio p. 923, July 30, 1919. 

Fiber Length and Position, by W. Codlitz. Paper TrapE JourNAL, Vol. 
Hom Nos ls pe oG. Jan. 6, 1921¢ 

Fibers as Related to Pulp and Paper, Structure of Wood and Some 
Other, by H. N. Lee. Pulp and Paper Magazine of Can., Vol. 
ISeNOS, ps 001, July te 1915. 

Fibers, The Characteristics of, by H. A. Maddox. Pulp and Paper 
Mag. of Can., Vol. 13, No. 21, p. 551, Nov. 1, 1915. 

Fibers, Differentiation of Jute, Manila and Adansonia. Paper Makers’ 
Monthly Jour., Vol. 57, No. 12, p. 367, Dec. 15, 1919. 

Fibers, The Length of Some Paper Making, by E. Sutermeister. Pulp 
and Paper Magazine of Canada, Vol. 12, No. 2, p. 43, Jan. 15, 1914. 

Fibers, Factors in the Measurement of Pulp, by J. H. Graff and Marie 
Hodgdon. Paper, Vol. 23, folio p. 333, Dec. 4, 1918. 

Fibers, Length of Wood. Paper, Vol. 26, folio p. 15, Mar. 10, 1920. 

Fibers in Paper, Estimating Percentages, R. C. Griffin. Jour. Ind. & 
Engr. Chem., Vol. 11, No. 10, p. 968, Oct., 1919; Paper, Vol. 25, 
folio, p. 463, Nov. 5, 1919. 

Filter Paper, Testing. Zell stoff u. Papier, Vol. No. 1, p. 61; May, 1921. 

Filter Paper, The Penetrability of, by R. C. Griffin and H. C. Parish. 
Jour. of Ind. & Engr. Chem., Vol. 14, No. 3, p. 199, Mar., 1922. 

Filter Paper, Notes on the Testing of, by J. Rigand-Monin. Papeterie. 
Vol. 42, p. 818 (1920). 

Folding Resistance, by W. Herzberg. Chemical Abstracts, Vol. 14, 
Deeez62, July. /20,41920; 

Folding Endurance of Paper, by F. P. Veitch, C. F. Sammet and E. O. 
Reeds raper. Vv Olu. 20. No. 12,.p. 13, May. 30, 19.17; 

Gelatin and Casein. Papeterie, Vol. 42, p. 122, Feb. 10, 1920. ; 

Glarimeter, by Kieser. Zellstoff u. Papier, Vol. 1, p. 113, July, 1921. 

Glarimeter, Instrument for Measuring the Glaze of Paper. Electrical 
World, Vol. 63, p. 645, Mar. 21, 1914; Pulp & Paper Mag. of 
Gait Viol— 12.5): 233, Apt. 15, 1914; 

Glarimeter, Improved, by L. R. Ingersoll. Paper, Vol. 27, No. 23, p. 
18, Feb. 9, 1921. 

Gloss of Photographic Paper, Measuring the. Paper, Vol. 26, folio p. 782, 
May 26, 1920. 

Graphic Analytical Method for Paper, by O. L. Gartland. Paper, Vol. 
25, folio p. 515, iwwov. 12, 1919. 

Groundwood, Phenylhydrazine Test for. Paper, Vol. 23, folio p. 31, 
Sept. 18, 1918. 

Humidity Affects Paper, How, by H. A. Maddox. Paper, Vol. 7, No. 
22, p. 4 (1911). 

Humidity, How Paper Is Affected by, by Otto Kress and Philip Silver- 
stein. Paper, Vol. 19, No. 25, p. 13, Feb. 28, 1917. 

Humidity, Physical Testing of Paper as Affected by, by Ross Campbell. 
Jour. Ind. & Engr. Chem., Vol. 9, p. 658, July, 1917. 

Humidity on the Moisture Content of Paper. The effect of, by Ross 
Campbell. Paper TrapE JourNAL, Vol. 73, No. 2, p. 30 (1921). 
Humidity on the Strength of Paper. Effect of, Papeterie, Vol. 41, p. 

455, Oct. 25, 1919. 
Humidity Testing Room, Description of a Constant Temperature and 
F. P. Veitch and E. O. Reed. Paper, Vol. 21, No. 23, p. 174, 
Eee 13, 1918; Jour. of Ind. & Engr. Chem., Vol. 10, p. 38, Jan. 
18. 

Iron Impurities in Paper, by H. A. Maddox. Pulp & Paper Mag. of 
Can., May 1, 1914. 

Laboratory, Notes on the Design and Equipment of Paper and Pulp 
Mill, by ‘“Snow-Shoe.”’ Pulp & Paper Mag. of Can., Oct. 1, 1915. 

Loading and Filling Materials, by Sindall & Bacon. Paper Makers’ 
Monthly Journal; Paper, Vol. 20, No. 7, p. 22, Apr. 25, 1917. 

Loading of Paper, Qualitative Determination of the. La Papeterte, Vol. 
41, p. 266, Aug. 25, 1919. 


122 


pa. 


72. 
PER 
74, 


im 
76. 


77. 
78. 
79. 
80. 
say 


82. 


83. 
84. 
85. 


86. 
87. 


88. 


89. 
90. 
a1, 
D2. 
93. 


94. 
GS: 
96. 


ie 
98. 
99. 


100. 


101. 


102. 
103. 


104. 


105. 


106. 


BIBLIOGRAPHY 


Microscope, The Use and Care of the, by E. Sutermeister. Pulp & 
Paper Mag. of Can., Vol. 13, No. 22, p. 576, Nov. tS.io na. 
Microscopic Analysis of Fibers, Modification of Iodine-sulphurie Acid 

Stain. Paper, Vol. 24, folio p. 707, July 9, 1919. 

Microscopical Analysis of Fibers. La Papeterie, Vol. 41, No. 1, p. 30, 
May 25, 1919. 

Microscopical Characteristics of Rosin, by James Scott. The Paper 
Maker's Monthly Journal, Vol. 49, No. 6, p. 671, Juste, 1915; 
Paper, Vol, 16," Noe 18; ps 2-13) July: 14, 190: 

Microscopical Examination of Paper Fibers. Paper, Vol. 29, No. 9, 
DP, 20s OV aaa ls 

Microscopical Work in Paper Testing, by E. M. Chamot. Jour. of Ind. 
& Engr. Chem., Vol. 10, No. 1, p. 60, Jan. 1918; Paper, Vol. 21, 
Nop 1 95-p-2d7- eban. VOumlo ke: 

Microscopy, Iodine Solution in Paper, by C. J. West. Paper TRADE 
JournaL, Vol. 73, No. 4, Aug. 4, 1921. 

Microscopy of Paper Fiber (C. G. Bright Stains). Paper, Vol. 20, No. 
25. puede Aug 29, 1917. 

Microscopy of Parchment Paper, by C. Bartsch. Papier-Fabrikant, Vol. 
16,.-p.2171201918)- 

Microscopy of Pulpwoods, by Eloise Gerry. Paper, Vol. 26, folio p. 277, 
Apr. 21, 1920. 

Mineral Matter of Paper, Analysis of, by J. Scott. Paper Maker & 
British Paper Trade Journal, Vol. 61, No. 4. 

Moisture on Paper Tests, Influence of. Paper Maker’s Monthly Journal, 
Voli260; 2NO.c1> pio. Jat Gea 922, 


Moisture on Paper, Effect of, Paper Maker’s Monthly Journal, Vol. 
57. Deol AGS, Lo, 219108 

Moisture on Paper Tests, Iufluence of. Paper, Vol. 29, No. 4, p. 16. 
Dees, 1921. 

Moisture Regain of Papers at Different Humidities, by Otto Kress and 
G. C. McNaughton. Paper, Vol. 22, folio p. 665, Aug. 21, 1918. 
Opacity, Factors in Obtaining. Paper TraprE JouRNAL, Vol. 50, No. 6, 
Paper Microscopy, by J. H. Graff. Paper, Vol. 23, folio p. 642, Feb. 12, 

1919, 


Paper Sizing, by Fritz Stockigt. Wochenblatt fur Papier-fabrikation, 
Vol, 1, p. 39: (1920); Paper, Vol: 26; folio p. i) Mare 10) 1920; 
Paper Testers, by D. C. Douty. Paper TrapE Journat, Vol. 50, No. 6, 

p. 259, Feb. 10, 1910. 
Paper Testing. World’s Paper Trade Review, Vol. 74, p. 26, Dec. 24, 
1920 


Paper Testing, by F. A. Curtis, Circular No. 107, Bureau of Standards. 

Paper Testing, Report of Committee of TAPPI, by F. C. Clark. Paper, 
Vol; 21, No. 6, p., 11, Oct..17,. 1917; Paper, Volo 21, Noss. ap eae 
Oct;- 24;-1917- 

Paper Testing, TAPPI Report on, by F. C. Clark. Paper, Vol. 25, folio 
p. 693, Dec. 10, 1919; Dec. 17, 1919; Dec: 24, 1919; Deco 3121919; 
Jansen, L920: 

Paper Testing, The Technique of, by H. A. Bromley. Pulp & Paper 
Mag. of Can., Vol. 13, No. 16, p. 439, Aug. 15, 1915. 

Phloroglucinol, Notes on the Chemistry of. Paper, Vol. 22, folio p. 641. 
Aug. 14, 1918. 

Photomicrographic Study of Paper, by E. A. Hunger. Paper, Vol. 20, 
Nov: 19) pals July 1818175 

Porosity of papers, Determining the. Paper, Vol. 22, folio p. 91, Apr. 
10, 1918. 

Porosity of Paper, Method of Testing Relative, by F. J. Seiter. Paper, 
Viol. 21, No. 2; p. 17,. Sept... 19, 1917. 

Pulps in Paper, Method for Differentiating and Estimating Unbleached 
Sulphite and Sulphate, by R. E. Lofton and M. F. Merritt. Tech, 
Papers, 189, Bureau of Standards. 

Qualities and Tests of Paper. La Papeterie, Aug. 10, 1919; Paper, Vol. 
25, folio p. 1112 Feb. 11, 1920. 

Qualities and Tests of Paper. La Papeterie, Vol. 41, p. 98, June 25, 
ee ee 41, p. 226, Aug. 10, 1919: Paper, Volesza.peie 4 
(1920). 

Quality of Paper, Methods of Estimating the, by F. C. Clark. Paper, 
Vol.c10,GNG27, palloe vane 9G. Lolo. 

Rosin in Paper, Quantitative Determination of, by C. F. Sammet. Jour. 
Ind. & Engr. Chem., Vol. 5, p. 732, Sept., 1913; Paper, Vol. 13, No. 
Lp SAs Septeehier wise 

Rosin Sizing, An Investigation of, by F. C. Clark and A. G. Durgin. 
Paper. Vol. 21, No: (235 p. 136,. Pebo 136, iss 


Size-Fastness, A New Test for, by Stanley A Okell. Paper, Vol. 20, 
No. 53 pe 20: April 31917. 

Size-Fastness, Okell’s Method for, by S. A. Okell. Paper, Vol. 22, folio 
p. 469, July 3, 1918. 


107. 


108. 
109. 


Se 


138. 


140. 


BIBLIOGRAPHY 123 


Size-Fastness of Paper, New Method for Determining the, by Fritz 
Stockigt. Wochenblatt fur Papier-fobrikation (1920); Paper, Vol. 
26, p. 1 (1920). 

Sizing, A New Test for, by C. J. West. Paper TrapE JourNnaL, June 
24, 1920. 

Sizing with Iodine, Testing for.. Jour. of Ind. & Engr. Chem. Vol. 11. 
PeeoeZ (1919). 

Sizing in High Grade Papers, Detection of Faulty, by C. F. Sammet. 
Circular No. 107, Bur. of Chemistry, Dept. of Agr.; Paper, Val 
LO SENG. O pred: Feb. 125 OTS. 

Sizing ‘of Paper, Research Work on the aby. beiGs-Clarksand Aq G- 
Durein; “Paper, Vol. 22, folio p. 223, May 15, 1918. 

Sizing Quality, The Determination of, by F. T. Carson. Paper TRADE 
JourRNAL, Vol. 74, No. 14, Apr. 6, 1922. 

Soda and Sulphite, Pulps, Differentiation of, by P. Klemm. Wochschr., 
Papier-fabrikant, Vol. 48, p. 2159. 

Soda and Sulphite Wood Pulps in Paper, Detection of, by R. Wasicky. 
AE alle Vol. 16, p. 212 (1918); Jour. Soc. Chem. Ind., 

Olaaoo 

Spots in Paper, Soot or Carbon. Paper, Vol. 17, No. 15, p. 15, Dec. 22, 

1915. 


Staining of Wood Fibers for Permanent Microscopic Mounts, by H. N. 
Lee. Pulp & Paper Mag. of Can., Feb. 1, 1917. 

Starches—Properties Useful to Mills, by G. M. MacNider. Paper, Vol. 
SO mNOG ep el Om late 4-6 L917. 

Starch in Presence of Cellulose, Determination of, by F. Kaulfersch. 
Chimie et Industrie, May, 1921. 

Starch in Paper, Estimation of, by O. Kamm and F. H. Tendick. Paper, 
Vol. 25, folio p. 460, Nov. 5, 1919. 

Starch in Paper, Quantitative Estimation of, by V. Voorhees and O. 
Kamm. Paper, Vol. 24, folio p. 1091, Aug. 27, 1919. 

Staining of Wood Fibers for Permanent Microscopic Mounts, by H. N. 
Lee. Batanical Gazette, Vol. 62, No. 4, p. 318, Oct., 1916. 

Strength of Paper When Wet, Determining the, by E. O. Reed. Journal 
Ind. & Engr. Chem., Vol. 8, p. 1003, Nov., 1916; Paper, Vol. 19, 
No. 11, p. 15, Nov. 22, 1916. 

Strength Tests for Paper, Description of a Paper Tearing Resistance 
Tester, by H. N. Case. Jour. of Ind. & Engr. Chem., Vol. 11, No. 
1, p. 49, Jan., 1919; Paper, Vol. 23, folio p. 509, Jan. 15, 1919. 

Sulphite and Soda Pulp in Paper, Test for. Paper, Vol. 24, folio p. 
Clyeewiay 7.1919. 

Sulphite and Sulphate Cellulose in Paper, Testing Methods for, by 
G. Schwalbe. Pulp & Paper Mag. of Can., Vol. 12, No. 1, pp. 
Ee 21, tan. 1, 1944: 

Sulphite Pulps. The Differentiation of, by T. B. Seibert-and J. E. 
Minor. Paper, Vol. 25, folio p. 1005, Jan. 28, 1920. 

Sulphur in Paper, Determination of, by E. Sutermeister. Pulp & Paper 
Mag of=Can.- Vol. 15,-No. 44, p, 1021, Noy. 1, 1917. = 
Tearing Resistance of Paper, Testing, by C. F. Sammet. Paper, Vol. 

20,2 holies p. 1053, Keb. 4, 1920. 

Tearing Resistance of Paper, by S. D. Wells. Paper, Vol. 23, folio 
pas v0, eb. 12,-.1919. 

Tearing Resistance Tester, A Paper, by H. N. Case. Jour. of Ind. & 
Engr. Chem., Vol. 11, p. 49 (1919). 

Tearing Strength of Paper, Supplementary Study of Commercial In- 
struments for Determining, by P. L. Houston. Paper Trape 
JournaL, Vol. 74, No. 10, p. 43, Mar. 9, 1922. 

Tearing Strength of Paper. World’s Paper trade Review, Vol. 75, p. 6 


Tearing Strength of Paper, Device for Testing the (U. S. Pat. No. 
1,273,972), by R. O. Wood, to A. D. Little, Inc. Jour. Soc. Chem. 
ind., Vol. 37, No. 21 (1918). 


Tearing Strength Test for Paper, by A. Elmendorf. Paper, Vol. 26, 
folio: p. 002, Apr. 21. 1920. 

Tensile Strength Tester (T. ah ie & Co.). World’s Paber Trade 
Review, Vol. 75, No. 5, p. 468. 

Tearing Test, Preliminary Study of Tearing and Tearing Test Methods 
for Paper Testing, by P. L. Houston. Tech. Papers, No. 194. 
Bureau of Standards. 

Testing of Paper and Paper Products for Specific Use, by J. D. Mal- 
colmson, The Paper Industry, Vol. 1, No. 2, p. 104, May, 1919. 
Testing Physical Properties, by S. W. Widney. The Paper Industry, 

Voli1,2 Now 75. pe .514,5 Octar 1919: 
Translucent Effect on Paper. Photometric Experiments of the. Jour. 
Ind. & Engr. Chem., Vol. 9, p. 184, Aug., 1917. 


Translucency and Opacity of Paper, Measuring the, by R. Fournier. 
Papier, Vol. 23, p. 259, Nov., 1920. 


BIBLIOGRAPHY 


Translucency of Papers, A Measurement of the, by C. F. Sammet, 
Circ. No. 96, Bur. Chem., Dept. of Agri.; Paper, Vol. 7, No. 7, 
p.. 22, May 1, 1912. 

Transparency of Paper and Tracing Cloth, Specifications of the. Circu- 
lar No. 63, Bureau of Standards. 


Vegetable Fibers Used in Paper Making, by F. C. Clark. Paper, Vol. 
23, folio p. 944, Feb. 26, 1919. 

Volumetric Estimation of Paper, by E. H. Hiarne, Papier-fabrikant, 
Vol. 13, No. 45, p. 709, Nov. 5, 1915; Paper, Vol. 17, No. 20, p. 14, 
Jan. 26;).1916. 

Water Resistance of Fabrics, by F. P. Veitch and T. D. Jarrell. Jour. 
Ind. & Engr. Cnem., Vol. 12, p. 26 (1920). 

Webb Paper Tester, by J. D. Malcolmson. Paper, Vol. 23, folio p. 976, 
Mar. 5, 1919; Jour. Ind. & Engr. Chem., Vol. 11, p. 133 (1919). 

Weight of Paper, Determination of the Apparent and Actual Unit. 
Papier-fabrikant, Vol. 17, p. 472 (1919). 

Witham Paper Tester. Paper, Vol. 24, folio p. 156, Apr. 9, 1919. 

Wool, Test for, by H. LeB. Gray, Jour. Ind. & Engr. Chem., Vol. 
10; -p. 633" C1918): 

Yellowing of Paper. Paper, Vol. 22, folio p. 1, Mar. 13, 1918. 

Yellowing of Paper, by A. B. Hitchens. Paper, Vol. 22, folio p. 553, 
July 24, 1918. 

Zinc-Chloride-Iodine Reagent and Its Uses, by F. C. Clark. Paper, Vol. 
7, No. 5, p. 23, Apr. 17, 1912. 


A 
Page 
PUSOTIION woo eo ee is ats 89- 90 
Wir Tesistanice: oceans ss rps 
PREIS OSDOES fain css oS 36 
Ammonium molybdate 
POPC CE adn RS 5 112 

Aniline sulphate ....... 24 
CW ale SP 2 Aga ge 41 
COS (POSS a 106 
Ashcroft tester ....:... by 

B 
OE FE SI a 44 
Basis weight scale ..... 48 
AN DAG a 25- 26 
Beating, degree of .. Abs 
PeOntine -testo.o, cies. . 90 
On ee 78 
ite te Stain (cae... 20 
MON Ei 56 
PUtOtr SPCCKS uuu s 36 

c 
aay tester <0. e050 6: 51 
Cady micrometer ..... 55 
er POMG ACI ok eee 117 
We ee a eke ca 110 
Chrome yellow ........ 117 
Classification of fibers 25 
Pra particles: ....is... 36 
LO ee a 108-109 
Mle ee a ae 104 
ale ISPOtS en oes re 36 
Coloring matter ....... 116 
SOeTIOTIOE pe 43 
Conducting particles . 97 
WE COCO as ck oh. 42 
(res Cirection....->.... 44 
Gererpetnod 4... a... 78 

D 
Dalen blotting paper 

OS ee ae 91 

Pyensomicter 2.23... .. 73 
Prt paper ......... 35 
Pot retOl va a 21 
PIPAVGBDOLS docs so 5 oc a's ae 
Dry indicator method .. 79- 80 

E 
Elmendorf tester ...... 72 
POP AUOH: Goa cia eres 41- 42 
‘Equivalent weights .... 50 
Estimation method .... Ze 
TOeMAUSION he. s cass ee 42-102 
Extensometer ......;.. 103 
PREP BCUOl oo. . viers hss os ns 98 


F 
Page 
Factors, conversion .... 50 
ATS Sastre Pee fy ss 1 
Fehling’s solution ..... 114 
Melrisid@a eta ec cree ec 45 
PEE heeds wreck on be, bk: 98-107 
Eiotation test)... 2... 76 
Ream Spots'e-, ob es 7 
Folding endurance ....41-42-58 
Formaldehyde .....<.: 118 
OUT CSGHee ap e0 ve oF « 78 
CCC oh Sie Fs 118 
G 
Glarimeter, Ingersoll .. 94 
RaLOSG tat cee rath Oalcaes tele te 94 
Grease resistance ...... 85 
Ground glass method .. 82 
Gunning method ...... 112 
H 
PEAIVEV INS) Eh ce wn 83 
Herzberg stain, ....."s%. 18 
FUME Ves eee ba 39-43-83 
Hygrometric state ..... 38- 40 
I 
Ink flotation test ...... 76 
Tron specks te Ors s65 35 
K 
Reese oe as Se a 37 
ON CAUSE ava wars cate 76 
bea Petiperes neue ayy Qoetel 
Lieberman-Storch ..... 110 
Loften-Merritt stain .. 20 
M 
Machine direction ..... 44 
Microscopical examina- 
EPG Tart ae rote ale sek - 16 
, Millon method>...2.0. ss 110 
M. I. T. folding tester . 62 
Wi Gisthive a Awsme:s -42-106 
Mullen test yeas. eee. 41 
N 
Nitrogen, proteinaceous 112 
O 
OHS ER ie Mae ain Masons 117 
OL SHolears eres eects 36 
Okell ein, ey ak pak 76-77-78 
Pact y ante aan eee 


125 


126 INDEX 


P Spence and Krauss ... 22 
Page Stains, special “2 aanaeem 24 | 
Paper v Specks onc eus ns 37 Starch 24 dso 37-113-14 
Paratin ies 4 cee 116-117-118 Stem fibers ..)..00eee 25- 27 
Para-mitroamiine +2; .. 25 Stiffness. . 5. (75. eee 105 
Pea and beam scale ... 49 Stockigt =. /2 ae 76- 81 
Penescope 26 ies 89 Sulphur: ¢ 3... pee 115 
Perkins tensile tester .. 46 Sutermeister stain .... 18 
Permeability 4 kk 43 
Phidroglucinol 27.426. 24 A 
Physical testing ....... 38 Tearing resistance ...42-43-68 
Prussian Diues ook eee 117 Temperature 27) seo 38-43-83 
Tensile breaking 
Q strength sae 41-42-64-67-68 
Muadrant- scale. 45%, 5 46 Texture, surface ...e8 96 
Thickness 930.0) eee 55 
R Torsion: balance. een 47 
Raspail methodan< 723. 110 Trade custom sizes .... 48 
Rag Ac Fi can Poe 52 
Resin specks 2-5 ses an 110 U 
Retention of filler .... 98 Ultrantarines. Gone 117 
Rosinespecks¢< yong 2 35-110 
Rubber specks (...<..4 3o V 
S Volumetric composition 96 
Salievite acids S225 a 117 W 
Samplitip see ss, o 12 Water resistance tou se 81 
DICALES orcs ute eee 49 Webb | tester, “i.e ame a3 
Schopper cj ne 58-65-74-102 Weight 47440 (Geer 40- 45 
Seed: hair fibers ....... 25- 26 Wet “rub. ae ya 
Sizing, degree of ...... 76- 81 Wire sides en eee 45 
Sizing. suriace 73,5 ae 82 Wheatstone bridge .... 77- 78 
Sriatts ie Ges ven aes nee 116 Wood. specks" i ue 35 


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